Launch a browser with overmind open

[bradgessler]

I use overmind for all of my projects and find myself wishing I could type in overmind open after running overmind start and have it automatically launch a browser with the port of the running app on localhost.

If this feature is too specific for something that overmind would consider implementing, a JSON formatting option when running overmind status that shows ports would make it easier to write a script that accomplishes this functionality.