Bump Analytics API version to 0.26.1

Takes advantage of fix for bug where number of items in request
to course_summaries/ was capped at 1000, causing a 500 error
on Insights home pages with close to or greater than 1000 courses.

EDUCATOR-464: Improve performance of CourseSummariesPresenter

CourseSummariesPresenter.get_course_summaries now passes required
course IDs to the course_summaries API call, reducing the size of the
returned list.

EDUCATOR-464

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* Update edx-auth-backends and fix imports

* Update dependencies and fix new pylint errors

* Switch to alternative django-waffle fork

Current django-waffle master does not support management commands in Django
1.10+. The maintainer seems to have disappeared and hasn't merged any PRs in a
year.

This fork fixes the issues, but hopefully it will get merged into master in the
future and we can go back to installing django-waffle from pip.

* Pull freshly installed docker image for tests

* Don't use option "on" with waffle flag command

* Upgrade to Django 1.11.2

Will it just work?

* Use class based LogoutView and set redirect url

The function-based views are deprecated in Django 1.11. Except for
logout_then_login, which is still okay apparently.

* Use dispatch instead of get on InsightsLogoutView

* Address PR comments

* Use 0.25.1 of data api (also upgraded to 1.11)

Update for release

Add passing learners column and put behind feature flag.

EDUCATOR-442 Remove footer's feedback email and all references to it

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* Added passing users to CSV behind enable_course_passing waffle switch.

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Add information about Programs filter to docs

Wrap long filter names and add some padding.

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