Add markdown rendering toggle for gists with markdown source type

Summary

When a gist is created with markdown as the source type, the content is rendered as raw source instead of providing an option to toggle between rendered markdown and source view. The user expects a textbox or toggle that allows switching between markdown source and rendered output, while preserving the ability to edit the markdown source.

Steps to Reproduce

1. Create a gist on DevPlace.
2. Select 'markdown' as the source type.
3. Observe that the gist content is displayed as raw markdown source.

Expected Behaviour

When markdown is selected as the source type, the gist should show a textbox with an option to choose how the content is displayed: markdown source or rendered markdown (result). Editing should still allow modifying the markdown source.

Actual Behaviour

The markdown content is rendered as source only, with no toggle or option to view the rendered result.

Environment

Not provided.

Reported by retoor via DevPlace.