When doing the functional tests use the new function
`projects.transfer` instead of the deprecated function
`projects.transfer_project()`

fix: use url-encoded ID in all paths

utils.EncodedId() has basically the same functionalityy of using
utils._url_encode(). So remove utils._url_encode() as we don't need
it.

fix: members: use new *All objects for *AllManager managers

Add EncodedId string class. This class returns a URL-encoded string
but ensures it will only URL-encode it once even if recursively
called.

Also added some functional tests of 'lazy' objects to make sure they
work.

Make sure all usage of the ID in the URL path is encoded. Normally it
isn't an issue as most IDs are integers or strings which don't contain
a slash ('/'). But when the ID is a string with a slash character it
will break things.

Add a test case that shows this fixes wikis issue with subpages which
use the slash character.

Closes: #1079

Change it so that:

  GroupMemberAllManager uses GroupMemberAll object
  ProjectMemberAllManager uses ProjectMemberAll object

Create GroupMemberAll and ProjectMemberAll objects that do not support
any Mixin type methods. Previously we were using GroupMember and
ProjectMember which support the `save()` and `delete()` methods but
those methods will not work with objects retrieved using the
`/members/all/` API calls.

`list()` API calls: [1]
  GET /groups/:id/members/all
  GET /projects/:id/members/all

`get()` API calls: [2]
  GET /groups/:id/members/all/:user_id
  GET /projects/:id/members/all/:user_id

Closes: #1825
Closes: #848

[1] https://docs.gitlab.com/ee/api/members.html#list-all-members-of-a-group-or-project-including-inherited-and-invited-members
[2] https://docs.gitlab.com/ee/api/members.html#get-a-member-of-a-group-or-project-including-inherited-and-invited-members