Resolve "Option for lecturers to add guidelines/checkboxes for TAs to sign off or grade students."

Closes #129 (closed) and #110 (closed)

Also:

• Upgrade ChihuahUI to 1.0.2
• Description now shown in assignment page
• Description supports markdown (https://commonmark.org/help/, https://confluence.atlassian.com/bitbucketserver/markdown-syntax-guide-776639995.html)
• Can add guidelines (with markdown support) for signing off assignments.
• Feedback supports markdown.
• Write tests

Description on assignment page

Guidelines on feedback panel

Feedback supports markdown