* issue.event_count to digested_event_count
* event.ingest_order to event.digest_order
* issue.ingest_order to digest_order
This is generally more correct/explicit, and is also in preparation
of doing work on-digest (which may or may not happen)
* IssueStateManager.mute
* IssueStateManager.unmute (from Issue.unmute)
* more tests for alerts
* unmute moved to IssueStateManager
* create_unmute_issue_handler moved-over to models.py