Disable everything but GET except in Shorten and (deprecated) Pastebin. (See below).

A look at production logs shows that this won't hurt anyone, but
it is a breaking change. Basically in preparation for the Haskell rewrite, I'd
like to drop supporting non-GET on most of our controllers.

Before:

ricky@t520 ~/devel/php/dagd (master)$ http --body PUT da.gd/ip
98.27.131.138

After:

ricky@t520 ~/devel/php/dagd (master)$ http --body PUT dagd.local/ip
405 - method not allowed

ricky@t520 ~/devel/php/dagd (master)$ http --body GET dagd.local/ip
127.0.0.1

This is a trial - I'm going to deploy this and make sure nobody complains.
If it breaks anyone and I'm made aware, I'll revert it. If I don't hear anything
within a few days, I will assume that this change is fine and keep it.