Update structure, some names and imports

[andrii-balitskyi]

Closes #54 and #55

[andrii-balitskyi]

@razor-x We have a circular import error with these changes. How do you think we should restructure the code to fix this?

[razor-x]

I don't know if this will fix things, but ideally the tests only need to import from the public API, e.g., instead of from seam.exceptions import SeamApiException it should be from seam import SeamApiException.

Meaning, importing anything like seam.* is NOT supported for consumers of this lib even if python allows it (can we prevent that usage?).

I understand if some unit tests need to import things that are not exposed on seam, however I can't think of any cases like that. And in those cases, we can write the test files alongside the module.

[andrii-balitskyi]

@razor-x I fixed SeamApiException imports in tests but circular import issue didn't go away. The issue is that seam/models.py imports AbstractRoutes and Workspace from seam.routes.models then seam/routes/__init__.py imports AccessCodes from seam.routes.access_codes and seam/routes/access_codes.py attempts to import AbstractSeam from seam.models, which is already being loaded, hence the circular import error.

[andrii-balitskyi]

Closing in favour of #63