Add XWiki UI standards to the edit inline sheet of the SVN configuration pages

The inline edit form of the SVN Config class does not follow the XWiki form conventions.
A consequence of this is that it doesn't display page wide and some fields are difficult to edit because of this (e.g. the default spaces list has a small place in the UI to be edited).

We should make it a proper xform full to display nicely and easy to input.