v1.21.3

-- -- Step 2 of changing the way Homer3 stores the group data in memory, how it saves processed data and loads processed and acquired data. Clean up and simplify Calc() method code for generating tHRF_Common in GroupClass and SubjClass.

-- Update Homer3 to preserve capability of handling .nirs files and generating group level processing output.

-- Change the way unit test code modifies AppSettings config file and then restores it to original, in order not to have to revert change for AppSettings.cfg every time after running unit test.  Add userInterrupt function to be able to interrupt a long-running unit test with a Ctrl-C and have it automatically revert to original AppSettings.