Fixed background issue on some machines

Fixed background issue occuring on systems with OpenGL < 2.0 (NPOT background tile repeated in texture).

Solved "Failed to create texture..." problem

Solved "Failed to create texture, its internal size is too high" problem occurring on some machines.

Version sent for Gynvael's Summer GameDev Challenge 2017

Playable, but needs more levels and probably a couple of bugfixes.