Abandon the dicotomy frontend/compute nodes: support arbitrary number of group nodes, with an arbitrary number of nodes.
Update config file
Merge branch 'parinodes'
Rename configuration file from config.cfg to config
Rename `frontend_class` configuration option to `ssh_to`
Add `list-templates` subcommand.
Improve list-templates: now accepts an argument which should match the cluster template names.
replace `frontend_class` with `ssh_to` in documentation