Enable cider-jack-in on tramp buffers

When using cider-jack-in in a tramp source buffer, starts a remote nrepl
server, and connects to it. By default, sets up an ssh tunnel to the
remote port. This can be controlled using nrepl-connection-endpoint,
which defaults to nrepl-connection-ssh-tunnel.
Merge pull request #489 from hugoduncan/feature/tramp-jack-in

Enable cider-jack-in on tramp buffers