No more teapots.

Now that the ARI implementation is nearing some definition of
completeness, we should properly respond with 501's for unimplemented
functionality, instead of the almost humorous 418.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@395136 65c4cc65-6c06-0410-ace0-fbb531ad65f3