Feature: Level advancements

[bakbakbakbakbak]

Why? When a user changes the "level" field in their sheet, a dialog could ask them if they want to roll for HP and potentially on talents (if on a talent-level).

Notes Considerations of how to make this scalable with custom classes has to be taken. Are we going to introduce Class items that contain the talent table? #71

[Muttley]

I think this should really tie into whatever we do for character building

[PrototypeESBU]

This has been implemented as the level up app.