Add fallback shaders for low-end GPUs

[David Williams]

All volumes show up pink when using Cubiquity on Windows XP inside VirtualBox. This is possibly just a result of VirtualBox having limited 3D acceleration capabilities and not being able to provide the required shader support. We should probably provide fallback shaders for this situation, or at least check what to do to make Unity give more meaningful error messages (it currently complains about missing texture coordinates)

[David Williams]

This is a feature request rather than a bug, and so it being moved to Trello:https://trello.com/c/BkK2LdJK/7-add-fallback-shaders-for-low-end-gpus