Fix docstring typo and broken URL
Remove serialize_opaque_key since CourseLocator and friends contain that functionality now

See OpaqueKey. __unicode__() in opaque-keys/opaque_keys/__init__.py
https://github.com/edx/opaque-keys/blob/master/opaque_keys/__init__.py
readme: Expand workbench instructions
Merge pull request #77 from open-craft/dragonfi-documentation-update

readme: Expand workbench instructions
Merge pull request #79 from open-craft/fix-multiple-mentoring-blocks

Fix question repetition when multiple mentoring blocks present
Merge pull request #78 from open-craft/opaque-keys-follow-up

Opaque keys follow up
Fix submit button when multiple mentoring blocks present.