Add network_bridge Nodelet

[JWhitleyWork]

Currently the only way to include network_interface in a project is by using it as a library. While this is the most efficient method, it is not the most flexible. Adding the option to use a nodelet makes the nodes that rely on it more flexible (others can read/write the network message types) and almost as efficient as using it as a library without the need for the design-time decision.