lightcasters: Put common resources outside main.
lightcasters: Finally fixed the stupid bug direction changing bug.

   It seems that the delta (time difference between two frames) may
be negative, which doesn't make any sense. So clamping it to always
be positive fixed the bug.
   Also, since we've fixed that bug, we
don't need a workaround involving creating a singleton so we just
revert back to using a single function to load textures now
(see makeTexture in common.h).
lightcasters: Refactored scene to a class + fixed wrong window ratio.
lightcasters: Change background to slightly more black.