Add lesson drag and drop

[mslwang]

Implementation Description

Brief summary of PR

Screenshots

Visual depiction of PR

What should reviewers focus on?

Testing Procedure

• What test(s) should we run to make sure your code works?
  • What ways could the input be wrong?
  • Is it secure? Could nefarious users access/break it?

Things to Note

• Additional dependencies/libraries you've added?
• Things you'd want to know when coming back to the code after a few months

Checklist

• Ensure code follows style guide by running the linters
• I have updated the documentation or deemed it unnecessary
• I have linked the relevant issue in this PR
• I have requested a review from the PL, as well as other dev(s) (and designers if necessary)

[mslwang]

TODO: Fix jumping transition animation issue due to this beautiful dnd bug: https://stackoverflow.com/questions/59130533/items-jumping-when-dropping-on-react-beautiful-dnd