Adding customization options to the helper gizmo.

Helpers can now have their color customized and have six more options for shapes: Dot, Cross, X, Circle, Polygon, and None. The new shapes respect multidimensional scaling, so permutations such as ellipses are possible.  An additional cross and/or X can be drawn on top of the selected shape, allowing further differentiation between otherwise similar helpers.  Helpers can also have their size frozen so when the scene camera zooms in/out the absolute size of the helper remains the same on-screen.