Make DB Import backwards compatible

closes #2716
- Continues to parse and allow import with the old format
- Detects the presence of the new JSON-API format and allows import
Merge pull request #2719 from appleYaks/import-backward-compatible

Make DB Import backwards compatible
Add try-catch to startup

- Should prevent Ghost from exiting without an error message
Clenaup API index.js, and add docs
Refactoring API arguments

closes #2610, refs #2697

- destroy expects an object, rather than an id all the way down to the model layer
- all API methods take consistent arguments
- route params such as :id, :slug, and :key are passed as an option & used to perform reads, updates and deletes
- browse, read, destroy take options, edit and add take object and options
- HTTP posts api can find a post by slug
- Add API utils for checkData