Fix import loop (circular import)

[davidculley]

I wanted to write an unit test but couldn't because I encountered an import loop (meaning: before you can finish importing A you must import B, but you can import B only after you finished importing A, so the import fails because it would result in an infinite loop).

This pull request fixed that problem.

Here's an explainer of the problem and why this pull request is necessary:
https://www.youtube.com/watch?v=UnKa_t-M_kM

[dae]

The fact that it doesn't work out of the box is unfortunate. It used to - this broke when pylib switched to an implicit namespace, which means we can't run any code when the base module is imported. A simple workaround is for calling code to import anki.collection first. The other imports should then import correctly.

I'm not sure about this PR. Importing a submodule as a separate symbol is not something our codebase currently typically does, and having to prefix types like NoteId is not ideal.