Updated package.json to conform to npm standards

fixes #1053

- fleshed out script object 
- added test and install package.json
- updated contributing guide


Just a note, the package.json shows the entire thing was updated but that's whitespace changes, probably mostly reverting the whitespace changes that were introduced in https://github.com/TryGhost/Ghost/commit/4e5c624d9f721983a0a7a729f0824b96bb94dd46.