Add delayed processes as a new argument starting overmind

[kiskoza]

Hi. I love your tool and using it for day-to-day development. I've run into only one use case that I wasn't really able to get working, and it's the "not always required" / "delayed" processes.

Let me give you a quick example of what do I mean by that: I have a react native repo where I need to work sometimes. It has a few processes that I would like to start with Overmind, but it also has the emulator that I don't need that often. Currently the only option is to set this emulator to be an ignored process (I don't want it to start every time I'm opening the project), but then overmind restart emulator won't recognize the process and won't be able to start it later, so I need to stop all the other processes and restart overmind when I need the emulator.

My change request is trying to solve this scenario: let's just start a noop script for these "delayed" processes than can die immedialety and then you can overmind restart xy / overmind stop xy whenever you need these processes.

Let me know if this makes sense to you or if I need to make any further changes to have this as a viable feature.

[kiskoza]

I think it solves #112 as well, or at least gives a better option than restarting the whole