A plugin must:

 - have a initialization function at <module>.start_up()
 - Provide each command at <module>.cmds.*
 - So far must provide the following commands:
      - pl_switch: <module>.cmds.pl_switch Power line switch on/off a device
      - pl_dim: <module>.cmds.pl_dim  Power line dim a device
      - pl_bri: <module>.cmds.pl_bri Power line bright a device
 - A script to populate the database with the protocol info, that is:
      - Protocol name
      - module name: the name of the python module that implements the plugin
      - validate_address_function: The path in dotted format to the valida_address
      that validate an address in the scope of the domotic protocol.
