refs #10187. Start refactoring processing logic

Make the same methods available for group processing as well as individual workspace processing.
refs #10187. Start modifying for processgroup overload.
refs #10187. Not fixed yet.

Looks like there's an issue with the m_filehandler not being initialized properly for some reason!
Merge remote-tracking branch 'origin/feature/9866_mdhisto_to_matrix'
Merge branch 'master' into feature/10187_process_groups
refs #10187. Need to open the group first.
refs #10187. Fix SaveNexus.
refs #10187. Bug in test code.
refs #10187. History tracking fix.

The history tracking object must be initialized whether we are processing
groups or not.
refs #10187. Old gcc compiler complains about init order.
Merge branch 'feature/10187_process_groups' into develop