Fix shape_utils genRIB function to use streams correctly.

fixes #290
Adding a PullDown widget to our HUD in examples/common

- adding pulldown type menu selector
- updated shape selection to use the new widget in various Gl examples
Additional GUI updates to GL example code

- switch Compute selection to pull-down menu
- add TBB controller to ptexViewer
- small cleanup in Hud

note: shading should also switch to a pull-down
More cosmetic changes to the examples GUI

- switch shading radio buttons to pulldowns
- re-ordered elements on screen in most viewers

note: the ptex viewer has not been updated to the new look yet
Adding a NO_MAYA flag to CMakeLists to disable all Autodesk Maya dependencies in the build
Cosmetic fixes to the ptexViewer example GUI

- switch to pulldown widget
- move GUI components around
- add TBB as a compute controller
More cosmetic fixes to examples' GUI

- fix default selection for pulldown widgets
- move widgets around to prevent overlap in examples
- add a little triangle indicator to the pulldown widget
- switch color from white to yellow for selected pulldown item