enhance `cider-connect` to auto-detect running repls on local and remote hosts

Two main changes:

 - `cider-connect` now interactively asks for host from a combined list of
   machine-wide ssh configuration and `cider-known-endpoints`.

 - Once the host has been selected `cider-connect` locates all running instances
   of lein servers. The machine must have `ps` and `grep` programs in the bin
   path.