Add top-level wrappers to the management pages

Containers analogous to ``#yarr_con`` on the list_entries page, named for the associated templates.

These are useful as styling hooks.  In my styles, I use them to apply padding to the container which is not present on ``#yarr_con``.

I didn't indent the content of feeds.html because it would explode the diff, but I'd be happy to amend the PR to do so if you like.