Added method for formatting a single value.
Added numeric value into menum items for setting min/max thresholds with right-click menu on histogram.
Fix a few items on Map Palette Settings: (1) Fixed step value set to 1% of data range for 'Fixed' spin boxes; (2) Added step value set to 1% of data range for threshold spin boxes; (3) Threshold slider were not enabled when 'Unlimited' range.
WB-405: Adding linking of high and low thresholds
WB-405: Fix synchronization of thresholding sliders and spin boxes.  Update tooltip for threshold link checkbox.
Changing theshold values was not triggering PaletteColorMappings modified status.  As a result, scene creation  not adding the modified palette status and thus scenes did not restore correctly.
When a scene is restored, close any overlay settings and palette map eidtors since the files they contain may no longer be valid.
QGLWidget::grabFrameBuffer()  on Mac appears to grab the 'back buffer' so when capturing an image, call QGLWidget::grabFrameBuffer() twice to fix image capture.
Resolved WB-471 Reload Layer to Constructor Dropdown.
For WB-471 Reload Layer to Constructor Dropdown: Update any visible overlay and map settings editors since they may contain the file that was reloaded and its palette may have been modified.