Dekko don't run with Qt5.12

Description

Work is in progress on an update for Qt to version 5.12. There are user reports that after updating to the new Qt version, Dekko will no longer run. https://forums.ubports.com/topic/4839/testing-the-upgrade-to-qt-5-12/82

@nanu-c gave the hint that the problem is probably in the quickflux. Here one would have to update to a newer version. https://github.com/benlau/quickflux/commit/93b07b55fd347f1ac5226c8ee3563016c5520acd