Texture: Add 'Order of Texture Commansa' and their semantics to API doc .. due to lot's of confusions.
GLJPanel: Add remark about FBO / GLSL texture-unit usage in API doc; Add API entry to set/get texture unit (default 0).

Allowing a user to set a specific texture-unit and to query the used texture-unit,
allows one to avoid a collision w/ own texture programming .. i.e. removes the burden to setup all params etc.