Define a network configuration API for ONOS

Define a generic model/mechanism. How the network behaves?

Provide one network configuration mechanism.

As a network operator, I need to be able to configure the network environment as well as the behaviour of the controller and/or of network control applications with respect to the environment, so that I can I can effectively manage the network.

Configuration should be:

• centralized
• distributed
• durable
• modifiable at run-time
• dynamically extensible

Implementation Notes:
We need to define what's the network model for ONOS with the help of Thomas and the other ONOS developers.
This will be fundamental when:

• we will refactor the configuration module for ARP/SDN-IP
• we will work on the use-case (for SDN-IP) of the host inside the SDN network communicating with/reachable by outside networks.