Fixed dynamic GUI background

Your main problem was mismatch between vertex screen and texture coordinates. Like assigning UV coordinates (t.x,t.y+t.h) to screen coordinates (r.x+r.w,r.y) which is a different corner. The end result is that your textures were flipped/rotated and obviously didn't scale correctly.

There was also some mess in drawGuiContainerBackgroundLayer which i fixed ;)