Scroll the user to the top of the form on submit

This patch the uses the ScrollTopCommand command.

For some reason, this command is contained within the Views module (even though it's not particularly Views specific functionality). This means we have to add the views_ajax.js to the page in order for it to work (otherwise there will be JS errors).
I've added a soft dependency on the Views module, so that the library and command are only added if it's enabled. It's not the cleanest, but will work for most people (as I can't imagine there will be many sites that will have Views disabled). For those that do not have Views, the functionality will remain as it currently is.

We also have to wrap the success message in the same wrapper, to allow the command to scroll somewhere.

New patch which simplifies how the container is added and also accounts for cases where a different selector is being used.

One last change. Was actually rendering the element with the 'render_selector' id (which is actually where the element should be replaced).

Got rid of that, and then moved setting up the container to where the $output array is started (think this is a bit clearer).