Add qute:settings handler

Add a page to make finding/setting configuration settings a little easier on
users. Tested changing different types of settings to make sure they all change
and retain the changes over a close/open cycle.
This has changed with the object registry - do you feel like doing these changes (i.e. ideally rebase on master?) or should I?

From the top of my head, you can do something like:

    cfg = objreg.get('config')
    frame = objreg.get('webview', scope='tab').page().mainFrame()