refs #827
- Moves ./index to use Ghost in a similar manner to how someone uses
Ghost as an npm module.
- Allows Ghost to be cleanly mounted on another express application
on any arbitrary endpoint, all you need to customize is the mount path.
closes#3789
- Create a GhostServer class to manage state
- index.js now calls start on the exported server
- Alter tests to expect a GhostServer instance
