Provide necessary information for experimental optimisation

[BenMoon]

Additional to the blob-count, I would like to see some additional numbers and graphs helpful for optimising an experiment optionally displayable in the GUI, e.g.:

• number of ions per time unit as a number and graph, optionally configurable as per shot (trigger) or time-unit (seconds)
• 2D histogram with selectable axis (tof vs tot, tot vs x...)
• histogram of cluster size, tot
• add frequency of trigger
• add slow updating ion counter (e.g. ions per minute)
• open pre-defined folder where data is saved (See Save pymepix viewer application state #17)

[troehling]

@BenMoon Can this be closed with the changes I implemented in #7, #8, #9, #12 and #13? Or is there anything that is not covered with the current implementation?

[BenMoon]

I think the

• trigger frequency
• open pre-defined folder where data is saved
• (ToT vs x)
  are still missing.