BREAKING CHANGE: remove deprecated project.issuesstatistics
in favor of project.issues_statistics

Convert our manager usage to be done via type annotations.

Now to define a manager to be used in a RESTObject subclass can simply
do:
      class ExampleClass(CRUDMixin, RESTObject):
          my_manager: MyManager

Any type-annotation that annotates it to be of type *Manager (with the
exception of RESTManager) will cause the manager to be created on the
object.

The 'managers' are dynamically created. This unfortunately means that
we don't have any type-hints for them and so editors which understand
type-hints won't know that they are valid attributes.

 * Add the type-hints for the managers we define.
 * Add a unit test that makes sure that the type-hints and the
   '_managers' attribute are kept in sync with each other.
 * Add unit test that makes sure specified managers in '_managers'
   have a name ending in 'Managers' to keep with current convention.
 * Make RESTObject._managers always present with a default value of
   None.
 * Fix a type-issue revealed now that mypy knows what the type is

Adding type-hints to gitlab/v4/objects/projects.py

Sync the create attributes with:
https://docs.gitlab.com/ee/api/projects.html#create-project

Sync the update attributes with documentation at:
https://docs.gitlab.com/ee/api/projects.html#edit-project

As a note the ordering of the attributes was done to match the
ordering of the attributes in the documentation.

Closes: #1497

Fix the import ordering using isort.

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