Configure online editor

[ErikSchierboom]

In Exercism v3, students can now choose to work on exercises directly from their browser, instead of having to download exercises to their local machine. The track-specific settings for the in-browser editor are defined in the top-level "online_editor" field in the track's config.json file. This field is defined as an object with two fields:

• "indent_style": the indent style, either "space" or "tab".
• "indent_size": the indent size, which is an integer (e.g. 4).

You can find a full description of these fields in the spec.

The "online_editor" field should be updated to correspond to the track's best practices regarding indentation.