Move glEnable/glDisable calls for texturing

from RenderingContext to StatusHandler_glCompatibility
Move boundTextures to CoreRenderingStatus

- Move MAX_TEXTURES to RenderingParameters.h
- Call glBindTexture in StatusHandler_glCore
Issue less GL calls by checking the data first
Do not store the check numbers as array

The check numbers are only accessed individually and there is never the
need to have them stored as an array. There, replace the array by
individual variables. Futhermore, initialize all members in the
constructor.
Order groups alphabetically
Replace two loops by only one
Code clean ups for texture unit usage group

- Remove unused function getTextureUnitUsages
- Use functions operator= and operator!= of std::vector to simplify the
  code