[Fix #828] Fix completion issues and don't forget current project directory in `cider-connect`

  - Add default values to fix `ido-ubiquitous` and standard `completing-read`
  - Look into current project directory for `nrepl-port` files
  - Generalize and rename `nrepl-default-port` -> `nrepl-extract-port`
  - Make sure that ports are always found in the right host (when connecting from
    remote files to localhost, or connection to different remotes than the
    current file's host)