Using target_include_directories for the sake of less code.
Using macro for less code.
Fix non-android build.

FindSDL2 exports the SDL lib separately from it's dependencies.
Adapted GLEW submodule to use target_include_directories and
target_compile_flags.
Fixing tests.
Update travis cmake with self provided packages.

Conflicts:
	.travis.yml
Fixing freetype-gl++
Improve SDL2_image CMakeLists
Improve SDL2-mixer CMakeLists.
Merge branch 'android-cmake-cleanup' into android
Organizing the cmake files better.