dodistribute: allow mass delete of keys

[slowriot]

Sometimes a large number of keys may have been submitted by mistake, or is no longer valid. Currently it seems the only way to remove keys is by clicking the x next to each one, and then clicking "ok" in the box that pops up. This is unusable for situations where you have to remove a hundred or more keys... such as those mangled by issues #60 and #59.