Fix a number of doc errors and warnings.

* Document a few missing classes/functions/methods
* Fix a number of QML snippets that wouldn't work as standalone snippets
* Add files to .pro so they show up in Creator..

Still the mysterious lack of controls dir documentation persists :/

Change-Id: I57162371a4d966e4db5bdb1b71d1baf9c0ca57c3
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>