Sokoban: enable the plugin for the c200. Invent a new, a bit more rockboxish colour...

Sokoban: enable the plugin for the c200. Invent a new, a bit more rockboxish  colour scheme since the old one didn't work in the small size that was needed for the c200's screen. Also use these colours in existing bmps and add some in-between sizes (e.g. for the Nano and Gigabeat) to use the screen size as best as possible. Rename the existing colour bmps consistently. Remove the drawing code for monochrome screens and let them use the bitmap build system too. This also allows further simplifying the code and let the plugin retrieve the tilesize from the bitmap.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@17569 a1c6a512-1295-4272-9138-f99709370657