Add default settings after registration

[jankapunkt]

Once a new account has been registered, users should not immediately be navigated to HomeScreen but should be asked to personalize a few settings:

• choosing a theme (light; dark; high-contrast; default = light) - this implies such themes exist!
• choosing voice (male vs female) - this implies there are multiple voices available
• choosing a default TTS speed (default=1)
• optional skip all these settings (defaults will be used)
• save settings in user doc on the server

These settings should also be available in the UserProfileScreen