Muon Separator: Monitor Spark Count

As a muon scientist, I need the Separator spark count to monitored, so that I can be alerted if the Separator is sparking excessively.
Before starting this wait for a spark in the data to analyse.

#### Acceptance Criteria
1. I can view the spark count.
1. Each spark event is logged (MINOR event)
1. I am alerted if sparks occur too frequently (Nagios alarm)
1. Excessive sparking is logged (MAJOR event)
1. sparking is excessive (LED is lit, red); otherwise LED is unlit.
1. I can reset the spark count to zero.
1. log the reset event (INFO event)
1. excessive sparking LED is unlit.

#### Notes
1. required by #3072
1. These [criteria](http://www.facilities.rl.ac.uk/isis/computing/ICPdiscussions/Muon%20FE/Muon%20FE%20Separator%20Criteria.docx) define the Separator spark count.
1. If the Separator PSU is switched off, the system should not count sparks (because there won't be any!).
1. When the Separator PSU is switched on, the system should reset the spark count to zero.