Unified attrib-creation/selection UI

[johnnyquest]

Attr Visualizer, Attrib Ramp, Attrib Shape SOPs:

• types: unspecified, float, int, vector, vector4 (menu strings: ''. 'f', 'i', 'v', 'p')
• class: detail, primitive, point, vertex (menu strings) -- in the same exact order (to match AttribVOP SOP param)
• compositing: replace, add, sub, mult, div, max, min
• attrib name selector popup menu should detect and show attribs of all classes and types, and should set all related parameters accordingly on selection

[johnnyquest]

there's a first version of the attrib selector menu --

shows:

• data type, in vexpression format (i@intattrib, f@floatattrib, v@vectorattrib, etc...)
• attribute name
• optional display of attrib class (e.g. point, primitive, etc.)
• "misc" qualifications string (if exists)