In triggered mode, Sweeper now coordinates image acquisition.  Compiles but untested.
Sweeper now explicitly keeps track of low many sweeps have been acquired, lowest/highest sweep index, and signal browser gets this info from the Sweeper.
Camera temp view in ImagerView is now updated after setting the setpoint temp.
Added ability to calc DF/F, sum over ROI, in addition to mean.
Fixed bug with ROI index handling.
Started implementing background feature.  Not done.