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

Sometimes we have errors where we don't get a dictionary passed to
RESTObject.__init__() method. This breaks things but in confusing
ways.

Check in the __init__() method and raise an exception if it occurs.

Fix the import ordering using isort.

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

Be more strict and don't allow untyped definitions on the files we
check.

Also this adds type-hints for two of the decorators so that now
functions/methods decorated by them will have their types be revealed
correctly.

Always create RESTObject._short_print_attrs with a default value of
None.

This way we don't need to use hasattr() and we will know the type of
the attribute.

fix(types): prevent __dir__ in RestObject from producing duplicates

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

Add the attributes: _create_attrs and _update_attrs to the RESTManager
class. This is so that we stop using getattr() if we don't need to.

This also helps with type-hints being available for these attributes.