[VitalSource] Enable customers to create their own VitalSource assignments

[chrisshaw]

In our demos, we'd like to let teachers go through the assignment creation flow. This will also be absolutely necessary to use in Spring pilots.

Questions:

• [x] Why can't a teacher go into Hypothesis today and use their own account to create an assignment? I get the sense we need to ask VS about this?

Scenario

:bust_in_silhouette: As an instructor

• logged into my LMS
• logged into a VS account I own
• using a book that VitalSource has given H access to

I can do the following:

• I copy a vitalsource link of a book I own
• I create a new Hypothesis assignment in my LMS
  • :information_source: you can assume canvas for now, but this should eventually work in content modules in other LMSs
• When I open the H file picker, I can see the button to select a VitalSource book
• I select the button
• When I put in the copied VS link and hit enter, I receive a confirmation message that I can use this book
• When I hit submit, the chapter selection and assignment creation flow works as usual

Notes

• Notice this doesn't actually say it works for students. It should, but if we discover in testing it doesn't, we should use in a separate ticket. This alone adds value by letting us test with teachers.

[chrisshaw]

The only restriction should be #1255 .