Add better development tutorial

[OnionKiller]

Current development tutorial may be not enough, or even misleading.
There may be double implementations of board games, where board game wrappers are not correctly used.
Development guide is missing, but there should be a list of what functions you are supposed to implement.

[fraknoiadam]

While writing the tutorial, we should also rethink what should we refactor, that could facilitate the development. E.g.

• Relay does not work without layout.tsx #63
• Set the init value of currentProblem greater than 0. (This one does not work currently.)
• Display all the math problems under each other, so we could easily check, whether every problemtext is correctly displayed.