[Rock-dev] Changes to some of the supervision model resolution behaviour

[Sylvain Joyeux]

I implemented some of the changes we discussed in the supervision 
tutorial. Namely:

  * all data services and devices must be referred to explicitely, i.e.

    Devices::Hokuyo (in short: Dev::Hokuyo)
    DataServices::Position (in short: Srv::Position)

    just saying "Hokuyo" or "Position" will not work anymore

  * the :provides option to data_service_type or device_type is not
    accepted. You must use the provides statement in a block (as shown
    during the tutorial, as e.g.

    data_service_type 'Pose' do
       provides Srv::Position
    end

  * you can (but do not have to) provide a Srv:: or Dev:: (or
    DataServices:: / Devices::) prefix in data_service_type, device_type
    and driver_for, i.e.

       driver_for "Dev::Hokuyo"

    is equivalent to

       driver_for "Hokuyo"

    It just reduces the confusion, as device models must be referred to
    as Dev::Hokuyo in the rest of the spec.

Sylvain