Tidy names and locations of modules

- Rename old "model_management" directory to "model_management_OLD" in order to catch
  dangling references to original model manager.
- Caught and fixed most dangling references (still checking)
- Rename lora, textual_inversion and model_patcher modules
- Introduce a RawModel base class to simplfy the Union returned by the
  model loaders.
- Tidy up the model manager 2-related tests. Add useful fixtures, and
  a finalizer to the queue and installer fixtures that will stop the
  services and release threads.

tests/conftest.py

@@ -1,7 +1,2 @@
 # conftest.py is a special pytest file. Fixtures defined in this file will be accessible to all tests in this directory
 # without needing to explicitly import them. (https://docs.pytest.org/en/6.2.x/fixture.html)
-
-
-# We import the model_installer and torch_device fixtures here so that they can be used by all tests. Flake8 does not
-# play well with fixtures (F401 and F811), so this is cleaner than importing in all files that use these fixtures.
-from invokeai.backend.util.test_utils import model_installer, torch_device  # noqa: F401