Merged old Box code with new Widget (untested)
Merge branch 'scenegraph_reorganization' into grid_widget
Widget updated to include margin, padding, border drawing, and child widget management
Implemented Texture3D class
Include Texture3D throughout shader.py, program.py and variable.py
Minor changes to textures.py
A bit of clean-up
Added testing for 3D textures
fixed Texture3D and added simple gradient example
Almar's fixes to Texture3D - glextTexImage3D and glextTexSubImage3D renamed glTexImage3D and glTexSubImage3D
Make it a bit easier to work on website

`python make website` gives the commands you can use, but also
emmediately clones the website repository

`python make images` clones the images repository so that the
website builder can build the gallery.
glsl-function: wip
glsl-function: with name mangling
Merge branch 'master' into grid_widget
function-glsl: more work
Incorporating new ideas from discussion on gitter. Also some
cleaning
glsl-function: tests!
minor fixes
Moving toward having canvas manage fbo / viewport and associated transforms
Canvas now keeps track of fb_ and ndc_transforms
viewbox1 example runs
Corrections for viewport setting in viewbox