Resolve "Add markdown editing buttons to the file editor"

What does this MR do?

Add markdown editing buttons to the file editor to insert proper tags for bold, italics, etc.

Screen_Recording_2018-12-13_at_10.54.41_AM

What are the relevant issue numbers?

Closes #27861 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Security reports checked/validated by reviewer