find sdl_image
added libRocket
added basic interface for displaying guis
allow rocket to use FAIO
allow rocket update to happen in game thread
Swapped out the need to use GLEW for SDL's OpenGL stuff.
replaced tabs with spaces + fixed compile error on linux
remove glew from cmake scripts
update travis to use sdl2
added cel/cl2 support to rocket backend
added gui manager class
remove sdl1 support

Conflicts:
	components/CMakeLists.txt
added input support for libRocket
fixed warnings
Merge pull request #82 from wheybags/gui

Gui framework
fixed bug when gui disabled
fixed error when compiling with CEL_DEBUG
fix issue where cels withoput headers were having incorrect widths computed
workaround for headerless images that contain transparency (eg data/option.cel)
Merge pull request #85 from wheybags/celfix

Celfix