Replace qtwebkit by qtwebengine

Qtwebkit javascript support is old and only runs very simple webview. Use it as webview engine doesn't suit well for an OS that want use HTML5 apps leveraging Angular and similar modern framework.

ctxnop and sdesneux made tests using http://mobileangularui.com/demo/#/ and almost all demos doen't works using webkit at contrarily of qtwebengine.

So qtwebkit should be replaced by qtwebengine waiting for a full chromium webview integration.