Use External Configuration File

**WIP**

This PR changes `test-status` to use a configuration file (`test-status.cson`) in the Atom configuration directory.

I've changed this because of the simple nature of the Atom configuration API. If you do not have a `test-status.cson` file, one will be initialised with the `DEFAULT_MAPPINGS` as defaults.

**Note I will be removing the majority of default file &rarr; command mappings.**

Related #31