Reduces size used for png files from 19,034,446 bytes to 13,305,798 bytes in total. The smaller files also improve loading times as the zlib decoder has less bytes to schlep through.
The PNG decoder shipped with OpenRA only supports a bit depth of 8 for images with a palette, so must must ensure that other depths (1,2 or 4) are not used.
zopfilpng is used for compression with the following command line:
'zopflipng.exe --keepcolortype -y -m image.png image.png'
The keepcolortype flag ensures the bit depth is not changed.
The trait documentation specified that the speed
and offset values are px/tick, but they have actually
always been treated as px/render.
Fix the update logic and rescale the map definitions
to account for the fixed behaviour.
