Add qrc protocol handler.

Support qrc resources in html. For example:
  <script type="text/javascript" src="qrc:///xx.js"></script>
  <image src="qrc:///xx.png"></image>

Change-Id: I490efb7cc300bf894659e79948b65729a12ad73d
Reviewed-by: Milian Wolff <milian.wolff@kdab.com>
Reviewed-by: Pierre Rossi <pierre.rossi@gmail.com>