Allow update of "ReplyTo" in article

"ReplyTo" (if present) overrides "From" when it comes to route a response
from OTRS, so it should be updateable as well to stay in control.

Added test cases for ArticleUpdate.
Fixed: Restricting process list by ACLs is only working with UserID (bug#10240).
Added a new central ObjectManager to simplify singleton object creation and usage. Thanks a lot to Moritz Lenz @ noris network.
Fix ::OM to also be available in object destruction.
Correctly set LogPrefix in InterfaceAgent.
Only use one global CacheObject.
Unified handling of Frontends.
Improved robustness of object destruction.

Squashed commit of the following:

commit 55d412ecf6738d654e9c3e38c33844e550983484
Author: Moritz Lenz <mlenz@noris.net>
Date:   Tue Mar 4 14:07:23 2014 +0100

    Properly clean out object manager at the end of the test

    otherwise the UnitTest's $Kernel::OM will take over at some point

commit 19c63a1ffcfe73defb0aa5ce4e1bbff8620f08ab
Author: Moritz Lenz <mlenz@noris.net>
Date:   Tue Mar 4 13:58:40 2014 +0100

    forgot to add Dummy2.pm

commit 789f8c6c8872531ce44053183c82a8917a164906
Author: Moritz Lenz <mlenz@noris.net>
Date:   Tue Mar 4 13:52:38 2014 +0100

    Improved robustness of object destruction

    Some objects create new objects in their destructor; thus
    several passes might be necessary to get rid of all referenced
    objects.
Fixed bug#10244 - No mouseover popup for fields in ActivityDialogs.
Tidied.
Tidied.
Make sure to only show the text directly in the label on using tree selection overlays.
Fixed bug#10264 -Description (espacially article description) in processes are shown on improper place.
Fixed bug#10264 - Description (espacially article description) in processes are shown on improper place.
Removed duplicate entry.
Fixed: Forward Email - not inline attachments with Content-ID (bug#8903).
Fixed entry.
InterfaceAgent; Fix "Invalid ChallengeToken"

The merge of the Object Manager branch caused a regression that caused
"Invalid ChallengeToken" errors, because the LayoutObject's intiialization
code ran in ->new(), but the information wasn't available
Code cleanup.
Merge branch 'interfaceagent-initialize-layout' of github.com:moritz/otrs