Make counters on tasklist filters consistent (#5470)
Summary: This implements my proposition from https://issues.kolab.org/show_bug.cgi?id=5470#c4
Reviewers: petersen, Roundcube Kolab Plugins Developers, vanmeeuwen
Reviewed By: Roundcube Kolab Plugins Developers, vanmeeuwen
Subscribers: petersen, vendel.colja
Differential Revision: https://git.kolab.org/D195