Intelligent switching between connections

 * cider-switch-to-relevant-repl-buffer: Never select wrong connection. When not
 sure ask the user. Register new connection locally. On C-u C-u interactively
 ask for connection.

 * cider-switch-connection: New command to interactively switch between
   connection. Allows *new* option which is currently delegated to
   cider-jack-in.