Define UBUNTU_USE_GLES variable to determine if the platform should use GLES2 or normal GL
add gl1 build-depends on non-armhf
add header boilerplate to config.h.in
Add ubuntu/ui/config.h with UBUNTU_USE_GLES so we can know whether to include GLES2/gl2.h or GL/gl.h.

Approved by Thomas Voß, PS Jenkins bot.