Make FormProcessView hybrid

[tleguijt]

At the moment FormProcessView expects an AJAX call and returns a JSON response.
This implementation is dependent on a Javascript form handling (jQuery-based example provided).
If the end-user decides not to use AJAX-calls (or forgets adding a javascript form handler) the view must also accepts normal post requests and redirect the user back to the original page with the formblock (and preferably scroll down to the form again using an anchor).