Fix various documentation issues

   - Replace multiple include statements with a single,
     Qt module include
   - Remove url variable (taken from the global config)
   - Remove indexes variable (using 'depends' is sufficient)
   - Remove unused subproject
   - Fix selector for QML types
   - Fix example path to have working manifest XML
   - Rename index.html to qtwebview-index.html (to avoid collision
     with the main Qt doc index page)
   - Fix section titles and add a 'QML Types' section for the
     QML module page.

Change-Id: Ie30582d8db83bfbdee613efec66013bb73d1a9b1
Reviewed-by: Christian Stromme <christian.stromme@digia.com>