BookReader Hypothesis support

[cdrini]

Work with @hypothesis to make bookreader integration with the hypothesis client fully work.

Will need a well defined fragment schema so hypothesis can treat BR more like PDFs.

Planning:

• [x] #1215
  • Fragment Spec: https://docs.google.com/document/d/1W6O_ASPOouMo_-USp9S0OCt9MGhIxG8eJe2eyA8CCuU
  • Project Plan: https://docs.google.com/document/d/1QLqwqo6lTOuWf2a0b2iK3_LOlseZ-vFtFBc3fCA8wqY
• [x] #1225 (2)
• [ ] #1234 (2)
• [ ] #1235 (2)
• [ ] #1236 (3)
• [ ] #1271

Other tasks:

• [x] #1270