Group song & setlist libraries

Invite other members (e.g. band, students, etc.) to a group library. From there you can have a shared song and setlist library. When one member creates a new setlist, it is automatically synced to everyone else. When one changes the order or makes a change, the same thing. You can also disable editing rights to certain members if you want (e.g. your students)

Changed the title from "App: Shared group song & setlist library" to "App: Group song & setlist libraries"

Merged "Ability to have multiple song libraries." #179

Merged "Allow folders for songs." #322

"I play in 3 bands and have a lot of songs. It would be nice to categorize songs by band (for example) so when I create a setlist I can view songs for only that band. Currently, I have to look through all songs."