Implement `ordering` challenge type

[mmcknett]

Describe the solution you'd like
ordering challenges are like multiple choice or checkbox challenges in that a list of options is shown. However, there are some key differences:

• The challenge has no options tag in its parameters. Instead, only answers is present. The UI is responsible for jumbling up the options that the student will reorder
• There aren't checkboxes (but you may need to render gripper affordances if you make the component drag/drop capable).
  Things that are the same: There's still going to be a "check answer" button, with feedback.

Important acceptance criteria:

• The options are not in the correct order to start (make sure either the parsing or the react component that renders the challenge jumbles them)
• There's some way of reordering the options. Drag/drop optional, but it would be the nicest experience.

Optional ACs:

• Support drag/drop to reorder the options
• Support drag/drop on mobile (i.e. drag/drop with touch works just as well as with mouse)