The type hints allow mypy to check the gui_hook calls, revealing a
bunch of places that are broken as they expect no arguments like the
legacy hooks.
To make mypy happy about PyQt's signal.connect(func), a qconnect()
helper has been added.
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)
