Removed obsolete Road contants classes and removed references to them
from factory class.
Improved racetrack system to generate segments with entities list only
if the seg actually has entities placed on it. On average half the
amount of total segs have no need for this list to be created and
wasting memory.
Added checkpoint sprite and distribution in levels.xml. Re-made texture
atlas.
Removed old sprite atlas stuff.
Moved RTObject classes to proto.
Added XMLs defs, parsing and checking for RTObject-based triggers.
Added basic implementation for triggering object triggers and segment
triggers.