Makes small changes in lms and cms both so that user's go to the
original page they intended to if they weren't already logged in

LMS-2644

* API endpoint for certificate generation, an authenticated  post with course
  id requests that grading be carried out and a cert generated for
  request.user in that course, using the usual grading and certificate
  machinery (ie, it does not imply whitelisting, though whitelists and
  blacklists will be respected)
  - Logs each request as it comes in
  - Calls xq.add_cert() and consequently, does grading synchronously on
    this app host and then queues request for certificate agent.
  - example usage:
    ```
    curl --data "student_id=9999&course_id=Stanford/2013/Some_Class" http://127.0.0.1:8000/request_certificate
    ```

* Studio advanced setting added, "certificates_show_before_end", which
  determines whether a course should permit certificates to be downloadable
  by students before the coures's end date has passed.
  - Modifications to dashboard view and templates to allow display of
    certificate download links before course has ended.
    (XXX: may declare failing students as failing before the course has ended.)
  - To test, turn the setting on in a course which hasn't ended yet, and
    force certificate generation for a student, then check their
    dashboard.

STUD-1558

Support incremental conversion of events from the old API to the new, in order to ensure the new system is working, enrollment events have been modified to make use of the new API.

JIRA: FOR-492

LMS-2479

Instead of noting users that are already in a cohort and not changing
such users, clobber the previous cohort and display a message indicating
the previous cohort membership.

JIRA: FOR-452

Instead of noting users that are already in a cohort and not changing
such users, clobber the previous cohort and display a message indicating
the previous cohort membership.

JIRA: FOR-452

LMS-2442

The old-style chinese language codes used in django 1.4 series are now deprecated, as discussed here:  https://code.djangoproject.com/ticket/18419.
Although majority of browsers still use the old-style language codes, some new browsers such as IE11 in Windows 8.1 start to use the new-style names instead of old-style ones which makes the current chinese translations of edX can't work properly under these browsers.
As there is no easy way for edX to change a higher version of django, I think we could do some mapping here so that the users who use IE11 in Windows 8.1 or other browsers that use the new-style names can view correct translations.
Also, this fix will make users who use one of the language codes:  zh-hk ,  zh-sg  and  zh-mo  can see the correct translations.

Pluggable InputTypes use edxmako.paths.add_lookup to inject new
mako template directories. Those were getting clobbered by microsites
(and by theming), which were completely rebuilding the mako template
lookup list from scratch.

This commit switches those two features to use the same add_lookup
function as pluggable InputTypes.

[LMS-2489]

Add some optional policies around password resets, such as password reuse, forced password resets, allowed frequency of password resets