Unassigning tickets now useses system trigger

- works around the limitaiton of needing to enable 'allow agents to assign tickets back to group'
- removes a suprising amount of code
- as an added benefit, adds in a confirmation that tickets have had their status updated when going into or out of the office
- actually needs only minimal changes to trigger and no new requests
removed readme mention of known issue
minor cleanup
clearer message for updating pending tickets
clearer message for updating pending tickets
Merge pull request #143 from ZendeskES/bevans/unassign

Unassigning tickets now useses system trigger