Support Flat frame jobs that pick exposure from the previous job, adjusts...
This MR supports Flat frame jobs that pick exposure from their previous sibling job, adjusts tooltips, and fixes exposure display in table. See #14 (closed) for more details.
This MR does a small change to the XML format with a new Flat Source (SOURCE_DARKFILTER) and a new Flat Duration (DURATION_SAME). Unfortunately, because of a bug when loading XML sequences, an unknown Flat Source will be considered to be a Dawn/Dusk source.
Tested load/save and flat duration computation, execution from Capture and Scheduler.