This rearranges the base template for the Change Form to prepare for

some updates to some of the settings and model pages.
The <form> is now the main container for the page's contents, and

contains the alerts (such as for form errors) and the content box. This

inverses the relationship these elements had before, in order to allow

alerts to more easily interact with the form (providing additional form

submission buttons, for instance).
The form alerts now have their own block called form-alerts,

positioned above the form content box. Templates that extend this

template can more easily add their own alerts in a standard place.

Tested along with some upcoming work on the repository configuration page.