Start processes from a config file

This define a helper command that load a JSON file and start the commands defined there using ```forever```. The format of the JSON file is an array of objects, being this ones the same format of the ```options``` field of the ```forever.Monitor``` object defined in ```forever-monitor``` project, with the only difference of an ```enabled``` field that when it's not defined or it's falsy allow to define a command on this JSON file but don't exec it.

This pull-request requires of https://github.com/nodejitsu/forever/pull/599.