Visual fixes for groups box

Moves and adds some stretches.
Fix up buggy group serialization

Tries to resolve several bugs with group state not being saved back to
database.
Move most group logic into router

This is going to be re-used by multiple callers, so it will work better
there.
Group playback support implementation

Allows the router to understand how to handle and perform callbacks for
a group of presets. With this, TTS tag group playback works.