Summary:
first step of optimization after the introduction of the dedicated proxy model.
already cleans up a lot of the interface and makes the Qml code easier. Performance does not seem to change much.
no functional change intended. all tests pass

Reviewers: #elisa, mgallien

Reviewed By: #elisa, mgallien

Subscribers: mgallien

Tags: #elisa

Differential Revision: https://phabricator.kde.org/D10271