Improve [Random] to use a custom mini browser

[Sarajiko]

added the ability to filter by course via "course__slug" for requests against the mini browser

See ownrecipes/OwnRecipes#11.

[sepulzera]

Please add the new query_param to the OpenAPI document.

Quick instructions:

1. Personally I use Stoplight Studio to edit OpenAPI documents. For Linux Mint, you can just download and run the AppImage.
2. Get the latest api dev: git checkout development and git pull
3. Make sure your user has write permission on the OpenAPI document: sudo chmod 666 docs/ownrecipes-api.json
4. Run Stoplight Studio and open the OpenAPI document (at the start screen, use "Open Existing Folder" at the lower left corner).
5. At the left sidepane, find the path "/recipe/mini-browse". Click on its GET.
6. Add a [+ Query Param] for your changes.
7. Save (ctrl + s) and do the git stuff.