Replace drop-down with radio buttons

Replace drop-down with radio buttons

Todal wanted a simpler UI for the single-article screen, rather more
like the version in the multiple-article screen. This does that, by
stripping out the old drop-down (and the thread status button), and
replacing it with radio buttons for all the approve/hold/reject
options.

Also, make it clearer that the "Comment" field is to go with the
rejection email to the poster.