Revert "Empty PixelMap::tick and put it in the constructor"

This reverts commit 2049b717c71be014f083934c5ff094c14738c4e9.
Revert "Empty Fill::tick and put it in the constructor"

This reverts commit 837c92d7c0f0311b2ab21d4b46582c1c085a7d64.
Clean up State subclasses; add color_t typedef
Make Board::read_state more sane
Remove Board class and put into main.cpp
Delete remaining State objects after tick execution