v1.21.6

-- Step 4 of changing the way Homer3 stores the group data in memory, how it saves processed data and loads processed and acquired data. Implemented distribute saving of derived data in separate files.
-- Add dataStorageScheme variable to DataTreeCass and make it a config option in AppSettings.cfg to be able to turn distributed saving of processed data on and off.
-- Remove testing of .snirf file with *_nirs user functions. Fundamentally incompatible. The *_nirs users functions should be tested only with .nirs files.
-- Reverse change to disable MainGUI when it is busy processing data, because there's a more optimal way to do this.