button groups instead of dropdowns for fast switching, resizing curve editing displays

[AndyQ]

In some UI areas, such as editing curves, it'd be much faster to have buttons to switch rapidly between editing selections - e.g. master/red/blue/green channels for curve editing - one click switching instead of click-move-highlight-click. Also, for curve editing in particular, it'd be nice to be able to resize the interface for more precise control. Interfaces with sliders can scale the length if you widen the panel, but the curve editor stays a fixed size - so how about letting us resize this panel vertically so the square edit area can get bigger? While your at it - curve editing would be nice with some detailed vector curve editing, like bezier handles and cusps, with right-click menus to change point types and delete points as per your normal vector shape editing.