Add trigger_time column to csv
Also add trigger time column to coincidence data
Update ProcessEvents subclass for ESD

Use ProcessEventsFromSourceWithTriggerOffset from SAPPHiRE
Fix name conflict
Update download date advisory
Add t_trigger column to data rows

This requires regeneration of ESD with that column.
Otherwise a KeyError will be raised.
Update Help page

Add info about Trigger Time.
Update some other definitions with, hopefully,
clearer information.
Slightly more robust updating

Also update histograms between ESD and coincidences

For coincidences and histograms:
Ignore stations/summaries when 'needs_update' is True
Improved (not perfect) cluster for coincidences

Still missing many detector locations.
And not date sensitive, just gets latest positions.
Merge pull request #60 from HiSPARC/trigger_timings

Include trigger timings in ESD by using the new class from SAPPHiRE
Combo class: ProcessEventsFromSourceWithTriggerOffset
Included in csv download