Clean up Settings page, hide unimplemented stuff
Bunch of quality-of-life updates:
- Fix message/recipient/session counters
- Fix showing database encryption status
- Fix showing "Show archived conversations" menu item
- Add showing/editing own profile in settings pull-down menu
- Move UUID and phone number from settings to profile page
- Only show profile UUID when in debug mode
- Hide page header when placeholder item is visible
- Hide bunch of unimplemented features from UI
- Remove unused/deprecated code