Add CSV format support for these SHOW commands [Issue: #12]:

- show_backup_servers
- show_pgsql_nodes
- show_backup_definitions
- show_snapshot_definitions
- show_restore_definitions
- show_backup_catalog
- show_restore_catalog
- show_job_queues
- show_backup_server_config
- show_pgsql_node_config
- show_empty_backup_catalogs
Bugfix: The parameter channel_check_interval is not supported. Update pgbackman command show_pgbackman_config to not try to show this information. [Issue: #15]