Added port flag to webpack-dev-server

[zacherkkila]

Obviously not a huge deal but this flag just needs to be set uniquely for each app if you want to run multiple dev apps at once (i.e. server and client program). Currently, if localhost:8080 is in use, the dev server starts on localhost:8081 and then grabs the index.js from localhost:8080.

This will instead throw Error: listen EADDRINUSE 0.0.0.0:8080, pointing you in a little more clear direction of what is going on