Refactor API arguments

closes #2610, refs #2697

- cleanup API index.js, and add docs
- all API methods take consistent arguments: object & options
- browse, read, destroy take options, edit and add take object and options
- the context is passed as part of options, meaning no more .call
  everywhere
- destroy expects an object, rather than an id all the way down to the model layer
- route params such as :id, :slug, and :key are passed as an option & used
  to perform reads, updates and deletes where possible - settings / themes
  may need work here still
- HTTP posts api can find a post by slug
- Add API utils for checkData