gl/WXGL* and gl/OSMesa* modules documented.

fsl/fsleyes/gl/globject.py

fsl/fsleyes/gl/osmesacolourbarcanvas.py

fsl/fsleyes/gl/osmesalightboxcanvas.py

fsl/fsleyes/gl/osmesaslicecanvas.py

fsl/fsleyes/gl/slicecanvas.py

fsl/fsleyes/gl/wxglcolourbarcanvas.py

fsl/fsleyes/gl/wxgllightboxcanvas.py

fsl/fsleyes/gl/wxglslicecanvas.py

fsl/fsleyes/views/colourbarpanel.py

fsl/fsleyes/views/lightboxpanel.py