upgrade how tips are retrieved for blocks that currently implement them

updated docs to reflect changes; consolidated tip output; slight tidy

fixed tests and style errors

tips is a list on read, not write

cleaned up tip transformer

added tests for new functionality

minimise diff

more style errors

version bump and simplify transform loop

remove unnecessary tips for mcq

remove tips from student_view_user_state

New course key migration script.

* Fix version number
* Make circle script more flexible for version bumps.
* Remove vestigial tests.
* Use find_packages in setup.py.

OC-2959 freeform and MCQ submitted values are a json and not an array

Bump version to 2.7.1.

Add simple test for MRQ student_view_data 

Add docs about API methods which can be used form native apps

[OC-2874] Added choices and tips to MRQ student_view_data

They are the same as the fields found under MCQ student_view_data,
except that this is for MRQ.

Some properties which depend on user state have slipped through initial
review, so I'm removing them now.

Bumped version to 2.7.0

[MCKIN-5253] Added student_view_user_state handler

[OC-2856] Fixed deprecation warnings for the Answer and Share models

Add student_view_data to step builder

Enable mobile support

Add API for native mobile Problem Builder + MCQ view to Problem Builder

Add 'name' attribute to AnswerBlock's student_view_data.

It will be useful to be able to get the names of all answer blocks in a
course via the Course API.