Small window behavior changes

PreviewCell no longer has a while loop. Instead, it will only close when
user closes it (remove "close" button in favor of window "x").

Also, tried to correct "legend doesn't show plot.name" error. Works most
of the time if you set "LegNumRows" property appropriately first. Can
always get it do display by resizing window with mouse...
Preview non-"rampable" cells with warning

MenuBuild.vi now builds "Preview Cell..." into menu based on
"isVariable?". Then, MenuDo.vi passes "isRampable?" to PreviewCell.vi.
Since timing variables are ONLY set correctly in RampGenerate, columns
with isRampable=FALSE warn users when previewing their (single-point)
output.
Merge branch 'Add-Menu-Column'