Always show solutions after level completion

[matthiasgeihs]

First of all: Great game!

Now to my issue: I think it's very helpful to have the full solution shown at the end of a level. Sometimes, as a beginner, you don't know if you found a good way of writing a proof, or if this was just very clunky, and there is a way more elegant way to write things.

Suggestion: Show "proper solution" after each level, not just after some.

[joneugster]

Good suggestion! Similar in flavour to #239, maybe they can be addressed in one go at some point