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.