Still todo:
- Add separate module for GUI hooks
- Update the remaining runHook/runFilter() calls
- Document the changes, including defensive registration
Allows Anki to register a mime-type handler for .ankiaddon files
Other small collateral changes:
+ fix positioning issues with some prompts and progress dialog
+ add prompt titles where they were missing
+ add type annotations for AddonManager installation methods
+ explicitly import os in main (used to be imported via aqt.qt)
