Load custom levels from the forum

[andybalaam]

On mobile and PC, allow loading levels people have added to the forum.

Think about how to handle inappropriate/spam levels. Probably allow flagging from within the app. (Further protection can probably wait until this proves to be a real problem.)

Include a way of tracking which levels you have solved, including noticing that a level has changed since you solved it.

Nice to have (probably separate issue?): allow submitting solutions when you solve a level. Further: allow submitting non-solutions (e.g. as bug reports)?