SCT: Operation Dialog: Set Slot Values over Time Range
Bug Number: n/a
Release notes (y/n): Yes
For Release Nums: 7.2

This commit implements the "Set Slot Values over Time Range" operation for 
this SCT.  The implementation conforms to the specification documented here, 
with the minor difference described below:

Feature Analysis: LBAO 1.4 SCT Tasks, RiverWare 7.2, July 2017
R:\doc\sct\2017\LBAO-1p4-SCT-FeatureAnalysis.docx
http://cadswes2.colorado.edu/~philw/2017/Sct-Lboa1p4/SctTaskAnalysis1.html

... Section (3):
   Easier way to apply an entered value to a time range on a Series Slot, 
   with Interpolation option.

The one difference is that, instead of being available from only a single 
timestep selection, it is also available from a multiple cell selection within 
a single slot -- the operation dialog's time range is initialized from the 
cell selection.

The SCT's slot/timestep cell selection is updated as the user edits the time 
range within the operation dialog -- to the extent that the SCT time range 
includes that full range.

See this screenshot:
http://cadswes2.colorado.edu/~philw/2017/Sct-Lboa1p4/2017-09-19/SetSlotValsTimeRangeDlg1.png