Step Builder: Interoperability for scale and plot blocks

[itsjeyd]

This PR follows up on #77 and #78 which introduced plot and scale blocks, respectively. More specifically:

1. The changes make sure that plots can access data from scale blocks.

2. The changes make the process for obtaining references to rating and scale blocks consistent in Studio. This means that instead of having to

   • bring up the "EDIT" dialog
   • scroll down to the "Question ID" field
   • copy the contents

   course authors can now grab IDs from previews of rating questions:

   

   For scale blocks this behavior was already in place.

Testing

1. Add Step Builder to a unit.

2. Add two Mentoring Step blocks and a Review Step block to Step Builder.

3. Add two Scale questions ("Ranged Value Slider") to the first Mentoring Step block.

4. Add a Plot block to the second Mentoring Step block.

5. For each Scale question, grab corresponding ID from preview.

6. Bring up the EDIT dialog for the Plot block and add the following to the "Claims and associated questions" field:

   This is an important claim, 7cf9575c53d5abc43fddedc4b06ae1a835dd4bf3, 79020e44630e246077a2bce92f45562fe24769cd
   

   Make sure to replace the two hashes with the question IDs you grabbed in the previous step.

7. Publish the unit.

8. Complete the first step of the unit by submitting answers to the Scale questions.

9. Navigate to the second step. The plot should show the answers you gave in the form of a single point.

[Kelketek]

👍