bug: Check account manage auto-assign flag

Auto assign tickets to organization's account manager only if the flag is set and as
the last resort i.e topic or filters assignment takes precedence.
Merge pull request #1013 from protich/issue/auto-assign-account-manager

Account Manager Auto-assignment

References:
http://www.osticket.com/forum/discussion/77593/1-9-1-auto-assignment-to-the-account-manager

Reviewed-By: Jared Hancock <jared@osticket.com>