BUG: fix QtWebEngineProcess for extension manager on linux
QWebEngineProcess could not find resource paths due to an upstream bug.
The fix is not available until Qt 5.11, so work-around is to include qt.conf file next to the QtWebEngineProcess executable, setting the relative path to 'resources/'
https://issues.slicer.org/view.php?id=4544
upstream bug: https://bugreports.qt.io/browse/QTBUG-66346 fix: https://codereview.qt-project.org/#/c/220734/