Refactor classes

- Clean up the handlers so the config variables are set through lita (not a global var)
- Move the pull request listing out into it's own class
- Move aliasing out into it's own class
I'm putting it in a variable so I can check to see if it's populated in the following line:

```
raise "invalid params in #{self.class.name}" if response.nil? || github_token.nil? || github_organization.nil?
```