support local development of javascript actions

From @sjfink :
Consider supporting local deployment of a web server that can be hooked into whisk as a debug option for local compile-edit-debug development of actions.

I.e. suppose we provide an SDK which is a simplified version of a nodeJsAction web server, that a user could download and run locally. We'd also need some tools to support configuring the user code for this local server -- maybe a simple convention to require("user code") or something. Then if we could tell whisk to invoke this local web server instead of spawning a hosted container, we should be able to debug the user code locally, and then upload it later.