MUX: CAEN hexagon additions

• Combine 4 separate hexagon data files into one data file, one data block per detector within file
• Still a separate nxs with sample environment, but look at adding external links so can open sample environment nxs which loads separate hexagon files transparently.
• Also save the current event energy spectrum to file for quick view
• begin command that prompts etc. like other muon instruments and always starts both hexagons
• (issue with hexagon data file run numbers getting out of sync if a hexagon is offline, but if they all go to same single file that should no longer be an issue)