Starting to create the interface

I'm reusing the existing param server to implement the new API while I work on the backend using services.

Let's focus on the example and the parameter.h.

When you create a Parameter with a default value:
- if the parameter already exist, the existent value is used.
- if not, the parameter is created in the param server with the default value.

When you create a Paramter a Cache Policy must be specified. I've created Cache Policy and Non Cache Policy for the Parameter class. The non cache policy request for the value of the parameter every time a node requests it and the cache policy is automatically updated with the last value (this policy should use the subscribe method, now uses param::getCached() ).