BUG 14830: Fixed initial display of opacity function editor

The initial range of the scalar opacity function was not set
correctly. Added a property "ScalarRangeInitialized" to the
PiecewiseFunction proxy that indicates whether the scalar opacity
function was initialized. This is the same property added to the
PVLookupTable proxy that makes the color lookup table initial display
work correctly. Its absence from the PiecewiseFunction proxy was
causing this bug.

Change-Id: I72096e947c871bee6a8438abdf207639202fffae
Merge topic '14830_initial_opacity_function_display' into next

644f7df8 BUG 14830: Fixed initial display of opacity function editor