New: Added tests for ``RepresentationGenerator`` class.
Update: Renamed ``ReferenceExtension`` class to ``FileReferenceExtension`` in ``anima.env.mayaEnv.extension``.
Update: Renamed ``Representation.has_repr()`` to ``Representation.has_any_rerpr()`` in ``anima.repr``
New: Added ``FileReferenceExtension.has_repr()`` method in ``anima.env.mayaEnv.extension`` which checks if the given FileReference node has a representation with the given name.