Use repl buffer as connection buffer

  Ancillary changes:

 - new functions `nrepl-start-client-process' and `nrepl-start-server-process'.
 - `cider-init-repl-buffer' and `cider-create-repl-buffer' have clear cut
    separation of functionality
 - `nrepl-make-buffer-name` and all `cider-create-xxx-buffer-name` take explicit
    dir, port and host variables.
 - increase `nrepl-decode-timeout` to 0.025 for greater reliability
 - merge `nrepl--handle-process-output` into client process filter
 - remove `nrepl-connect' in favor of `nrepl-start-client-process'