Create default files and directories
First implementation of the PgBackMan shell to interact with
PgBackMan.

- Display, registration and deletion of backup_servers
- Display, registration and deletion of pgsql_nodes
- Commands quit, shell and help.

First implementation og the PgBackMan database schema

- All tables
- Functions for display, registration and deletion of backup_servers
- Functions for display, registration and deletion of pgsql_nodes
- Jobs_queue
Change old referances to pgbck name.
Command register_backup_job implemented
- Modified some functions so they can accept serverID and FQDN
- Modified some functions so they can accept nodeID and FQDN
- Add command show_backup_server_job_definitions
- Add command show_pgsql_node_job_definitions
- Add command show_database_job_definitions
- Get default config values via get_default_*_parameter() functions
- Add some RAISE EXCEPTION code in some pl/pgsql functions
- Add support for sending pgbackman commands as a parameter to the pgbackman executable
- Add support for updating backup_server_config via triggers when a new backup server is registered.
- Add support for updating pgsql_node_config via triggers when a new pgnode is registered.
- New function to get the value of a configuration parameter for a backup_server.
- New function to get the value of a configuration parameter for a pgnode.
- conn.cursor() moved to __init__
- Add support for sending pgbackman commands as a parameter to the pgbackman executable
- Prototype of pgbackman2cron using listen-notify
- Add get_listen_channel_names functions so pgbackman2cron
  can get the list of channels to listen to.
- Add functions get_backup_server_id() and get_pgsql_node_id()
- Fix listen - notify functionality
- Fix several typos
- Implement add LISTEN / UNLISTEN channel when we register or delete a PgSQL node
- Improve deletion of PgSQL nodes.
- Create class listen_channels()
- Create configuration file functionality
- Add function get_next_crontab_id_to_generate()
- Clean up some code in pgbackman2cron
- Add generate_crontab_backup_jobs function
- Add looging to pgbackman2cron
- Add only one LISTEN channel when a new pgsql node is registered
- Update job_queue if the update of a crontab file fails.
- Own signal in pgbackman2cron
- Global logger in pgbackman2cron
- Better error and exception code
- Add Logs class
- Div bugfix
- Better error and exception code
- Add Logs class
- Div bugfix
- Use a global pgbackman_db object in cli.py
- Split database.py in two files, one for normal operations to the database
  and the other one for the notify/listen connections, these connections have
  to be persistent.
- New backup server configuration parameters with pgsql bin directory information
  for different releases.
- Some more functions for pgbackman_dump.
Add pgbackman_dump prototype
First version of  pg_dump_users() function