Ability to move nodes between pages #72

It would be good to be able to move/copy nodes between pages. The handling for this will need to have a way for each node to specify its own custom logic.

e.g. moving a database will have different additional handling than moving a files node.

In the "Add node" page, add a "> Move from page" and "+ Copy from page".

The UI here will need some consideration. First, we show the normal page picker that we use in other places (e.g. the page link select in the database).

But, after choosing a page, it would be nice to pop-up a view of the page (or at least an abridged one) that lets them click a node to select it.