Ability to choose content type; upload files?

It looks like they are sent as GET parameters instead:


@southp found that this is causing "HTTP 414 - Request - URI Too Long" when posting lots of content to a comment, for example.

Ideally we could also choose the request format between a few different options:

- application/x-www-form-urlencoded
- multipart/form-data (allows uploading files for testing the "upload media" endpoints)
- application/json
- GET parameters (is this useful? maybe not)

Start by tracing how the React/Redux console builds and sends requests, especially the comment POST flow and the upload-media endpoint testing flow. Compare the current behavior with the four formats listed in the issue; done means long comments no longer become overly long GET URLs and the supported request formats can be selected, including multipart file uploads.

Written by the indexing model from the issue text.