INCR-406 python3 compatibility

INCR-448 Python 3 compatibility

INCR-343 Python 3 compatibility

JIRA:EDUCATOR-4435

Remove user cookie reset on Student Dashboard.

INCR-403 python3 compatibility

INCR-402 python3 compatibility

INCR-422 Python 3 compatibility

INCR-435 Python 3 compatibility

INCR-384 python 3 compatibility

INCR-386 python3 compatibility

INCR-415 Python 3 compatibility

INCR-327 Python 3 compatibility

The enrollmentStatusHash cookie value was created in commit f0030334
as an optimization, in order to determine whether the marketing site
needs to refresh the list of a student's enrolled courses with a
call to the LMS. To ensure that this value was kept up to date,
commit d7a7bcc1 reset the user's cookies every time they go to the
learner dashboard page (which used to be the next page loaded after
you enrolled in a course). This didn't just reset the
enrollmentStatusHash though -- it recalculated all the cookie
values, as if you had just logged in.

A number of things have changed since then:

1. Enrolling in a course now goes to that course's info/navigation
   page, rather than going to the student dashboard.
2. It doesn't appear that the value of enrollmentStatusHash is
   actually being examined anywhere -- it's set in a cookie on the
   LMS and read/written by the edX marketing front end code, but
   the value is never looked at to make any decisions.
3. The introduction of add_email_marketing_cookies (which triggers
   off of the CREATE_LOGON_COOKIE signal) has made cookie resets
   far more expensive, as there is a blocking call to Sailthru if
   you have that enabled in EmailMarketingConfiguration (which
   edx.org does). This can add over two seconds to the server
   processing time for the student dashboard at certain times of
   day.

Given this, I'm removing both the call to resetting the cookie on
the student dashboard page, as well as setting the value for
enrollmentStatusHash.

Add credit mode in support enrollment tool.

Pin pip-tools==3.8.0 because of bugs

Update dependency backbone.paginator to v2.0.8

Update dependency backbone to v1.4.0

Move secondary SSO login button.

INCR-411: Updates on Python 3.x

The `NoneType` object is not available from the `types` module in
python 3. This is a workaronud to deal with that.

Use `ascii_letters` instead which is a reasonable alternative for our
usecases.

Currently, enrollment support tool is only allowing support members
to change course enrollment only one of the two modes i.e. audit and
verified.To move a learner other than these modes,they need to ping
devops.To broaden the scope of enrollment support tool,changes have
been done so that enrollment would be changed to other modes as well.

PROD-305

add submission deadline methods in InheritanceMixin