Remove dependency on automatic identicons switch, to allow manual contact management
Add preference to ignore contact group visibility.

This is useful for e.g. DAVdroid users, as DAVdroid does not assign a
group for synced contacts at the moment. (See rfc2822/davdroid#48)
Use radio button for style picker (partially reverts 7eb7dd3)
Reorganize and cleanup preferences
Use unique _ID for removal (raw_contact_id may not be), fix "Remove"
button to remove all of the contact's photos.