Check for R0205 useless-object-inheritance

Check for W0611 unused-import

Check for C1801 len-as-condition

- Downgrade to glib2 2.56.2 because higher is broken on Windows 7
- Dont abort build if depchecker fails on some files

Otherwise mypy hangs because the file is to big

- Make _() available, so other modules can import it from i18n, we need
this because mypy cant handle _() in the builtins namespace

NetworkIncomingEvent defines base_network_events and generate() already

Fixes #9321

- Save reference to contact in a dict instead of iterating the whole model
- Sort roster only once after all contacts have been added to the roster
- Speed up get_gc_contact()

Fixes #9334