Using External Packages over Hubot Scripts

This PR is a discussion around the idea of deprecating the use of `hubot-scripts` as a single package for all scripts over beginning to use external packages for groups of scripts.

I think in the long term making people use external packages for hubot scripts is going to be best for the following reasons:

## Developing

You can work on your scripts in a local hubot instance's `scripts/` directory until you're ready to package up your script. This allows developers to also specify dependencies in the `package.json` for the script so end users won't have to fiddle around with specifying dependencies (a big win).

## Testing

People can choose to test or not test their scripts using their favorite frameworks and libraries.

## Usage

People can just specify the script package and version in their hubots `package.json` and never have to worry about dependencies and what not.

Discussion around this idea is welcome :+1: