Fixing bug 9756 - AgentTicketMove lock issues (Follow up of PR #127)

As discussed in PR #127 and in the ticket 9756 (http://bugs.otrs.org/show_bug.cgi?id=9756), this is the pull request that contains the implementation of the feature RequiredLock for the AgentTicketMove.

This should solve the issue discussed in the ticket 9756.