WIP: Copay Shell Integration

This pull request is a work in progress that includes the following adjustments to Copay for integration with [Copay-Shell](https://github.com/gordonwritescode/copay-shell):

* Modify `app.js` to not start server, but export the express application instance, so that copay can be `require()`d 
* Modify start script to use `npm start` which calls `server.js` which in turn requires `app.js` and starts the server
* Adds `shell.js` to client js that detects copay-shell context and begins listening for events from the native shell, which in turn delegates some behavior to the existing controllers

*apologies for the whitespace changes in commit*