Implement top-down bruteforce

[fyrchik]

When combining figures in bottom-up fashion, it takes too long time.
Partially, because we cannot throw out obviously wrong solutions early. E.g. when figure is already has too big height which exceeds the height/width of the result.

One of the solutions to this is not combining figures one-by-one, but rather "subtract" them from the result, failing if subtraction can't be done.