Mesh: Set NumTriangles in SetIndexData
Rectangle: Clean up Create implementation
Rectangle: Clean SetDimensions implementation
Frame: Working Create implementation
Frame: Overload SetDimensions with proper origin
ui/*: Tweak interfaces
Only Resizable/Draggable require an On* pure virtual method.
Anchor: Documentation for SetAnchor
Anchor: SetAnchor offset not negative
Anchor: Overload Bind