Make the "xform" tool/gizmo available for strip transformations in the sequencer preview window. Because of the amount of hacks needed to make the gizmo work nicely with multiple strips at the same time, it was decided to only show the translate gizmo when multiple strips are selected. This is because the transforms with multiple strips would appear buggy because of our lack of shearing support in the transform system. There is also currently no way to properly sync the gizmo drawing with the transform when using multiple strips. Reviewed By: Richard Antalik, Campbell Barton Differential Revision: http://developer.blender.org/D12729