messagelist: show complete taglist in tag combobox

Instead of using configfile to store tags to display simply show all
tags. Otherwise we had to update the list, if we update the tags from
the kolab resource.

KOLAB: #4053
gcc4.6: needs friend class declaration
qt4.8: annotation namespace changed

The annotation namespace changes woth newer qt versions:
old:
<annotation name="com.trolltech.QtDBus.QtTypeName.In0" value="QDate"/>
new:
<annotation name="org.qtproject.QtDBus.QtTypeName.In0" value="QDate"/>
Merge remote-tracking branch 'kolab/dev/ubuntu_12.04' into kolab/integration/4.13.0