Speed up TicketAcl

Implements two optimizations for TIcketAcl as outlined in http://lists.otrs.org/pipermail/dev/2013-December/002843.html

* if an ACL module states its possible return values with ReturnType and/or ReturnSubType, it is only run if necessary
* Only the information that is actually required for running the ACLs is fetched.

Note that the latter introduces a backwards incompatibility, because ACL modules are now required to declare what they need.