Add char. sheet to Library from the sheet itself

Having to go to https://gamersplane.com/characters/my/ just to do this one thing is a bit of a pain. I suggest a button next to the edit pencil and the favorites flag. That may or may not persist while in Edit mode.

There's another conversation to be had about what adding a sheet to the Library should actually do but that probably needs a separate thread.

Edited to mention the new favorites flag.