Make the ssf.Window process model configurable

[ColinEberhardt]

Via email from Leslie @ Tick42

I would like to propose making the ‘process’ model visible in the create window calls. As per your presentation, Electron (by default) offers a separate process per window and OpenFin offers a shared process (with some sharding to allow process expansion). I would like to extend the API so that the app can check the container capabilities. The app can also request a particular process model and containers can reject calls they can not support. This may require the introduction of ‘window group names’. Clearly the parameter should default in a sensible way so that most apps do not need to worry about this.

I think that is a very good idea. Once this PR is merged #207 we will have a consistent process model between OpenFin and Electron. This was the easiest way to create a uniform baseline, which we can then extend to accommodate different modes.