Dependencies: Switch to SDL2

Includes: SDL2 2.0.1 and SDL2_image 2.0.0
	removing SDL_gfx - VDrift/vdrift@99c485a
	changing Deployment to 10.5 - SDL2 won’t build with lower
Dependencies: Update Bullet to 2.82
Dependencies: Update cURL to 7.33.0
Dependencies: Update Boost to 1.55.0