PLAT-1899 Fix some issues running under Django 1.10+

PLAT-1900 Remove dependency on abandoned django-pipeline-forgiving

Updates course about date conditionals

Update to week streak display logic

Refactor of the CourseEntitlement Refund API to handle refund failures

Fix invalid certificate page for a11y and translation.

Invalid certificate page has hardcoded lang='en' for
html, that would cause a11y issue for other languages user.
Some of screen reader text is not under translation. This patch
would fix both issues.

LEARNER-3110

Allow customizing heartbeat checks

deprecate html setting for web certs and set to true by default

- Formatted date start strings can contain unicode, so six.string_types is a better `is_instance` check
- "end_date" is no longer a required key in the `get_course_about_section` dictionary, so that check can fail and is bad.

Dont require creds to read from cache bucket

[LEARNER-3629]

The CourseEntitlement Refund API will not respond with ERROR codes when
the attempted refund call to Ecommerce fails.

Fixes to CMS failures in Django 1.11 tests

SFE Version bump

Upgrade setuptools to avoid bug that prevents OpenStack requirements install

PLAT-1890 Fixed assorted ModifyingEnforceTypeWarning warnings

Ensuring div and not button inside link tag for a11y.

Bundles dashboard fix

Convert cms login.html to the require_page pattern in preparation for…

Add optional password reset failure emails

Show advertised start date on course details page

ENT-837: Fix styling of enterprise sidebar on registration page.

update help link in header

RE: pypa/setuptools#951

LEARNER-2437

Add screenshots