use nconf to allow json-based config

Environment variables feel a bit unwieldy in node. So i added json support. But i left environment variable support in. So now options can be provided in a number of ways with this priority:

1. Arguments e.g. ```node app.js --DESTINYGG_API_KEY=your_key```
2. Environment variable or .env file
3. config.json
4. hardcoded defaults (could be moved to a file)

I also used nconf to load the plugins.json file and added the "plugins" key in there so that it doesn't need to be set programmatically.

I'd like to help out with some of the bot core stuff too if you'll let me. Node is something i've only dabbled with in the past and i'd love to work on a bigger project.