Adds config state

This is my first formula, and my first pull request on github. Please be as nit-picky as possible as I am learning how to structure future changes in the process.
I don't think this can be pass. The right way is [1]
```
    - watch_in:
      - service: postfix
```
[1] http://docs.saltstack.com/en/latest/ref/states/requisites.html