The method Ability.issues_readable_by_user takes a list of users and an
optional user and returns an Array of issues readable by said user. This
method in turn is used by
Banzai::ReferenceParser::IssueParser#nodes_visible_to_user so this
method no longer needs to get all the available abilities just to check
if a user has the "read_issue" ability.

To test this I benchmarked an issue with 222 comments on my development
environment. Using these changes the time spent in nodes_visible_to_user
was reduced from around 120 ms to around 40 ms.

Implement #3243 New Issue by email

So we extend Gitlab::Email::Receiver for this new behaviour,
however we might want to split it into another class for better
testing it.

Another issue is that, currently it's using this to parse project
identifier:

    Gitlab::IncomingEmail.key_from_address

Which is using:

    Gitlab.config.incoming_email.address

for the receiver name. This is probably `reply` because it's used
for replying to a specific issue. We might want to introduce another
config for this, or just use `reply` instead of `incoming`.

I'll prefer to introduce a new config for this, or just change
`reply` to `incoming` because it would make sense for replying to
there, too.

The email template used in tests were copied and modified from:
`emails/valid_reply.eml` which I hope is ok.

/cc @DouweM #3243

See merge request !3363

Reduce instrumentation overhead

## What does this MR do?

This MR reduces the overhead of instrumented methods. See the commit message of 905f8d763ab1184dc0b1e4bf6f18d7981753a860 for more information.

## Are there points in the code the reviewer needs to double check?

Not that I can think of.

## Why was this MR needed?

The overhead of method call instrumentation was too great.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] ~~[Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)~~
- [x] ~~API support added~~
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5550

This reduces the overhead of the method instrumentation code primarily
by reducing the number of method calls. There are also some other small
optimisations such as not casting timing values to Floats (there's no
particular need for this), using Symbols for method call metric names,
and reducing the number of Hash lookups for instrumented methods.

The exact impact depends on the code being executed. For example, for a
method that's only called once the difference won't be very noticeable.
However, for methods that are called many times the difference can be
more significant.

For example, the loading time of a large commit
(nrclark/dummy_project@81ebdea5df2fb42e59257cb3eaad671a5c53ca36)
was reduced from around 19 seconds to around 15 seconds using these
changes.

* upstream/master: (45 commits)
  Replace reject_blocked with reject_blocked! in callbacks.
  Fix Project#to_param to keep invalid project suitable for use in URLs
  Update CHANGELOG
  Add feature specs for edit project settings
  Fix renaming repository when name contains invalid chars under settings
  Change requests_profiles resource constraint to catch virtually any file
  Allow skipping users in autocomplete
  Fix typo in CHANGELOG
  Update CHANGELOG
  Respective cache is now expired when creating a new branch
  Update CHANGELOG
  Unify HTML format in static error pages
  Make error pages responsive design
  Move color-logic into HipchatService#HipchatService
  Depened on exact version of SimpleCov when patched
  Refactor spam validation to a concern that can be easily reused and improve legibility in `SpamCheckService`
  Refactor `SpamCheckService` to make it cleaner and clearer.
  Submit all issues on public projects to Akismet if enabled.
  Submit new issues created via the WebUI by non project members to Akismet for spam check.
  Upgrade Bullet from 5.0.0 to 5.2.0.
  ...

Submit new issues created via the WebUI or API to Akismet for spam check on public projects.

## What does this MR do?

Submit new issues created via the WebUI by non project members to Akismet for spam check.

## Why was this MR needed?

Support for Akismet was added only to the API with !2266. This MR builds on that functionality to also check issues submitted via the WebUI for spam.

## What are the relevant issue numbers?

Related to:

- #5573 
- #5932 
- gitlab-com/infrastructure#14
- gitlab-com/support#61
- !2266

cc @stanhu @MrChrisW 

See merge request !5333

Generate coverage report from whole test suite

Extends our CI plan to merge all coverage results and generate HTML report.

See merge request !5018

* upstream/master: (38 commits)
  Remove useless new route
  Update gitlab-shell version to 3.2.1 in the 8.9->8.10 update guide
  Fix typo in Elixir CI template
  Add a spec for access_for_user_ids
  Fix typo in comment
  Rubocop offenses
  Optimize the invited group link access level check
  Incorporate review comments
  Optimize maximum user access level lookup in loading of notes
  Fix missing schema update for 20160722221922
  Whitelist 'Simplified BSD' license
  Fix a bug where forking a project from a repository storage to another would fail
  Remove inline scripts from import pages.
  Make branches sortable without push permission (!5462)
  Profile requests when a header is passed
  Upgrade database_cleaner from 1.4.1 to 1.5.3.
  Show release notes in tag list
  Fix expand all diffs button in compare view
  Add route for Import::GithubController#new
  Update CHANGELOG
  ...