WIP: Add su-v's 'clip to page' extension.
Extension to clip to page area, with quick setting and releasing of clips.
Up to now, I have always created an extra layer, with a large rectangle with a hole the size of the page in it, to cover things that go over the page border and still be able to work on them.
A corresponding functionality in Inkscape itself should be (relatively) easy to implement and could be a good alternative to adding this extension.