Start making the Maemo support more generic.

This includes:
    - decoupling deploy configurations from targets (Reviewed-by: dt)
    - adding a "Generic Linux" device type
    - splitting up the Maemo deployment step into small pieces that
      can be combined in different ways (and much more easily maintained)
    - adding a new version handler for pro.user files
      (Reviewed-by: Tobias Hunger)

Also:
  - Add and use an SSH manager class for easier connection sharing.
  - Make the SSH connection parameters a fixed attribute of the connection.