LP1207533 patron triggered events log

LP1207533 patron triggered events log

* first cut at schema
* setting context_user, context_library, and context_bib on action_trigger.event
  when building the environment
* toward UI
  The original interface still exists and is used when spawned from Item Status,
  but for the patron interface, the Other -> Triggered Events / Notifications
  action will now spawn a new tab with the new interface.
* data retention
  Break the link between actor.usr and action_trigger.event when purging user data
  or aging circulations (as best as we can; some textual links may exist in
  action_trigger.event_output--i.e. overdue notices)
* release notes
* live tests

Signed-off-by: Jason Etheridge <jason@EquinoxInitiative.org>
Signed-off-by: Mike Rylander <mrylander@gmail.com>