Rewrite Activity Tracker with theme support, add functionality to delete entries

[tGecko]

Added theming, implemented scrolling through items and deletion of entries in activity tracker.

Selecting Item	Deleting item	Item deleted

Items are deleted by setting the new column roms.deletion_id for the selected item to the highest corresponding play_activity rowid.

Added a tool to restore deleted items to Tweaks

Added a migration script to add the roms.deletion_id column if necessary. Closes #1326

TODO:

• [ ] update other places to respect the deletion_id column (GameSwitcher.. ?)

Testing:

Test the migration script Test deleting items Test restoring deleted items