By having `RequiredOptional` in the `gitlab.base` module it makes it
difficult with circular imports. Move it to the `gitlab.types`
module which has no dependencies on any other gitlab module.

Add and/or check type-hints for the following files
    gitlab.v4.objects.access_requests
    gitlab.v4.objects.applications
    gitlab.v4.objects.broadcast_messages
    gitlab.v4.objects.deployments
    gitlab.v4.objects.keys
    gitlab.v4.objects.merge_trains
    gitlab.v4.objects.namespaces
    gitlab.v4.objects.pages
    gitlab.v4.objects.personal_access_tokens
    gitlab.v4.objects.project_access_tokens
    gitlab.v4.objects.tags
    gitlab.v4.objects.templates
    gitlab.v4.objects.triggers

Add a 'get' method with the correct type for Managers derived from
GetMixin.

Fix the import ordering using isort.

https://pycqa.github.io/isort/

Convert _create_attrs and _update_attrs to use a NamedTuple
(RequiredOptional) to help with code readability. Update all code to
use the NamedTuple.

In gitlab/v4/objects/*.py remove usage of:
  * from gitlab.base import *
  * from gitlab.mixins import *

Change them to:
  * from gitlab.base import CLASS_NAME
  * from gitlab.mixins import CLASS_NAME

Programmatically update code to explicitly import needed classes only.

After the change the output of:
  $ flake8 gitlab/v4/objects/*py | grep 'REST\|Mixin'

Is empty. Before many messages about unable to determine if it was a
valid name.