FIX: Wrong opengl light flag
used GL_COLOR instead of GL_DIFFUSE
FIX: View setup error in custom configuration
Error was apparent in cave-emu configuration: views were missing output.
Error was caused by tiles being disabled due wrong view / tile viewport
intersection, caused by the fact that custom configurations did not have a
computed global canvas pixel size.

Now the display configuration always computes a global canvas pixel size
based on the maximum pixel viewport extent of all the tiles present in
the configuration.

A somewhat related fix in the Camera class, use the tile pixel size as
the canvas size to check if drawing is enabled in a custom camera tile.
Merge branch 'master' of https://github.com/febret/omegalib