Added color buffer for models and fixed MP debug

-For some reason color buffer was not implemented. This effectivly broke
everything from d3d_vertex_color to every draw_primitive() function. I
also made draw_vertex and draw_vertex_texture use bound color and alpha
(via draw_set_color() and draw_set_alpha()) as it is in GM. Otherwise it
is impossible to draw them.
-Fixed up motion planning debug functions and cleaned them up slightly