Reordering sections in the sitemap

[jamesprior]

I am looking for a way to reorder sections in a sitemap and I was not able to find it. All of the drag and drop operations for sections look like they are trying to move instead of reorder.

I've made a branch with a very basic up/down button to reorder, I can submit a PR for that but it is slow and perhaps not a good enough solution for the 4.0 release, so I added this issue to either document how to reorder sections or to update the existing drag and drop behavior to reorder sections