Automatic service activation

[drdanz]

Following this @traversaro comment on robotology/robometry#30, I believe that it would be a very good to have some kind of service activation like other middlewares (for example DBus).

Services could be registered by port, and whenever that port is requested by some other process (for example whenever query is called on the yarp server), if the port is not active, the relative process could be started.

The biggest issue here is that, being a distributed architecture, it is not as easy as for DBus to start the process. We could consider using yarprun or some other tool to start it.

[drdanz]

One option that we could investigate is to use the xinet daemon to start the services when a connection on the port is made