Only call displayInstruction when control is active. Remove instructions when control is disabled.
Add default parameters to the _mixin partial.
Display region on the map if it is provided.
declare mixin values as arguments.
Update cursor once the rectangle is drawn, but the rectangle control is still active.
Toggle off the control when no region is passed into the rectangle control.
Change the cursor to crosshair while drawing the rectangle. remove class when the rectangle is done.
Merge pull request #45 from ehunter-usgs/rectangle-control

Rectangle control help text and mixin params