Fix kolab cache sync issues
Summary: Use QRESYNC, get rid of "scheduled" cache reset, other small improvements
Reviewers: Roundcube Kolab Plugins Developers, vanmeeuwen
Reviewed By: Roundcube Kolab Plugins Developers, vanmeeuwen
Subscribers: vanmeeuwen, Roundcube Kolab Plugins Developers
Differential Revision: https://git.kolab.org/D1726