Provide interface to Parameter Server

[baalexander]

See rospy's interface for an example.

This could go under the root ros namespace in ros.js. Something like:

ros.ParameterServer = Backbone.Model.extend({ })

ParameterServer could override the default set and get implementations. It may make sense for ParameterServer to used statically, but the advantage of extending Model is others could bind to param changes (the ParameterServer would act like a cache for the ROS parameter server).