[1099114] AlertAvailabilityDurationJob interrogates a wrong duration interval
Make sure the query for availability changes uses a duration adjusted for
the agent time, not the server time.  This is done by now storing the agent
avail change startTime in the timer's jobInfo for the duration check job.

notes
- these duration check jobs do not survive server restarts, so we can assume
  the job's infoMaps will always have the new startTime set.
[1093822] RFE (offshot of JON3-42) : Allow automatic uninventory of dead / missing / removed resources
Incorporate review feedback:
- add plugin-descriptor flag for types supporting the MISSING avail type
- use that flag to disable non-supporting types in the admin view for
  setting the policy.
- add ability to automatically ignore missing resources, in addition to
  the initial commit which provided automatic uninventory.
- lots of end-to-end changes to support the new MissingPolicy setting.