Support server-based apps

[mhkeller]

The main issue here that needs working out is how to start and stop the sever. Let's say you have two Node-based server apps, they probably both use port 3000 so you couldn't start all servers on Aufbau launch — not to mention that wouldn't be terribly efficient to launch a bunch of server apps at once, that you might not use.

How it should work is when you click on an app, it looks to the app definition for a startCmd command, which will boot up the server. The indexPath should include the port so that should be okay. Similar to the external flag, the app should see if a startCmd field is defined and navigate to the full indexPath href instead of navigating to a file.

When you exit the app, it should kill that server process. I'm not sure about the best way to do this. Server apps don't often have an end command. Aufbau could detect the port and then kill the associated process perhaps. Open to suggestions.