Bugfix#8244 QueueView hides queues w/o unlocked tickets

Currently QueueView only allows to navigate to queues which have at least one unlocked ticket.
Once the queue becomes visible, it is well possible to switch between filters that show either
All open or just Unlocked tickets in that queue.

Encouraged by very positive feedback in the bugzilla ticket http://bugs.otrs.org/show_bug.cgi?id=8244#c4,
this PR modifies the behavior as follows:

All readable queues have both non-closed and unlocked tickets enumerated. The results are
presented in the "Queue Bar" in the same order as the filters. This overview continues to
be generated through the the IndexAccelerator backends which have been modified accordingly.
Their queries now count tickets grouped by lock, and the filtering/consolidation is done in
code, so they can return a complementary 'Total' field in addition to the existing 'Count'.

A bug that produced incorrect sum of the number of tickets in nested queues has also been fixed.