Slight tweak to search display
Beginnings of Delete Thing

Doesn't work yet, but UI is pretty much ready.

Note that only basic ThingStates can be deleted for now -- we don't
allow you to delete Properties, much less Types or Collections.
Tweaked definition of deletable

Occurred to me that it's better to whitelist what *can* be deleted.
Actions menu now respects more permissions

Since I now have the concept of "disabled", used that to disable Edit
and View if I don't have permission.
Delete Thing now seems to be working

Introduced the notion of success alerts, while we're at it.