Support Markdown in comments

[popzip]

Text formatting (Markdown support) for comments was not an original requirement for Samplestack (text formatting for Qs and As was a requirement and is currently implemented). The imported seed data from Stack Overflow also contains comments that have Markdown syntax. This is currently displayed in the app as plaintext for the markdown chars.

-> Consider enabling Markdown rendering for comments.

Proposal is to support markdown in comments without displaying the Markdown toolbar and preview tab.

(Note: There was previously an internal discussion on this: https://github.com/marklogic/samplestack-internal/issues/87)