Fixed: Statistics per agent also shows invalid agents (bug#10277).

Squashed commit of the following:

commit 468fa5d3ea6d191c0f197beea6aa38a2559dfef1
Author: s7design <otrs@s7designcreative.com>
Date:   Fri Mar 7 14:44:43 2014 +0100

    Added the same fix like in Ticket.pm  for  all statistics

commit 8032c58cdca79d708b0886851a5a320d0767d61d
Author: s7design <otrs@s7designcreative.com>
Date:   Thu Mar 6 00:49:08 2014 +0100

    Added config parameter for invalid Agent in stats, and added check for this parameter.
    If parameter is set and have value  "No" in stats is shown only valid Agent.

commit cda93bfd51d86e6718bca722efcebb836816d81c
Author: s7design <otrs@s7designcreative.com>
Date:   Tue Mar 4 16:23:17 2014 +0100

    [Bug 10277] Statistics per agent also shows invalid agents

    Cahnged UserList forselection  boxes in Stats module. It are shown only valid Agents.