Achievements

[miloszwasacz]

It would be fun if we added achievements. They can unlock some kind of reward e.g. new Themes.

[Nircek]

The achievement state should be stored in the database along the user data.

What about not logged users? We can somehow store their state in their cookies... @miloszwasacz What do you think about that?

Also, we need to have a list of achievements. So there's the first one:

• the first correct solution

[Nircek]

I'm clearing the milestone since this issue has low priority.