clear request cache to avoid memory leak

update to use https

delete courses in the same transaction as writing them

python3 compatibility

add test case for discussion_id already set in XML

This is a clone (copy) of CSMH's declaration and methods with an added
id of UnsignedBigInAutoField

We should be able to delete the save_history code, but needs testing.

Add error logging when capa failures happen

Put StudentModuleHistory into its own database

Bump out the primary key on CSMHE

This gives us a gap to backfill as needed.
Since the new table's pk is an unsigned bigint, even for people who don't
consolidate CSMH into CSMHE, the lost rows are unlikely to matter.

Remove StudentModuleHistory cleaner

Also remove its corresponding ACCESS_REQUIRE_STAFF_FOR_COURSE feature
flag.

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

The old line:

    from path import path

produced pylint errors because of the baroque way that path.py defined
"path".  We tried to get them to change how they defined it, but they
deleted the name instead: https://github.com/jaraco/path.py/issues/102

(Jason then changed his mind, but this is a better way to use path.py,
it avoids the pylint error at least.)

PLAT-484

Split modulestore throws duplicate errors if course locator is not unique.

With split, "name" returns "course" instead of the run name.

The existing pattern of using `override_settings(MODULESTORE=...)` prevented
us from having more than one layer of subclassing in modulestore tests.

In a structure like:

    @override_settings(MODULESTORE=store_a)
    class BaseTestCase(ModuleStoreTestCase):
        def setUp(self):
            # use store

    @override_settings(MODULESTORE=store_b)
    class ChildTestCase(BaseTestCase):
        def setUp(self):
            # use store

In this case, the store actions performed in `BaseTestCase` on behalf of
`ChildTestCase` would still use `store_a`, even though the `ChildTestCase`
had specified to use `store_b`. This is because the `override_settings`
decorator would be the innermost wrapper around the `BaseTestCase.setUp` method,
no matter what `ChildTestCase` does.

To remedy this, we move the call to `override_settings` into the
`ModuleStoreTestCase.setUp` method, and use a cleanup to remove the override.
Subclasses can just defined the `MODULESTORE` class attribute to specify which
modulestore to use _for the entire `setUp` chain_.

[PLAT-419]

Move modulestore config for tests to an importable location
Disable pylnt warning for lms imports in common tests
Refactor all testcases that loaded all xml courses
TE-610
TE-489

TE-489

Make sure that during the serialization, all opaque keys and their
references and serialized using the `unicode` function.

AN-3821

Refactor get_parent_locations STUD-1663

[LMS-2757]

This commit updates lms/djangoapps/courseware.

These keys are now objects with a limited interface, and the particular
internal representation is managed by the data storage layer (the
modulestore).

For the LMS, there should be no outward-facing changes to the system.
The keys are, for now, a change to internal representation only. For
Studio, the new serialized form of the keys is used in urls, to allow
for further migration in the future.

Co-Author: Andy Armstrong <andya@edx.org>
Co-Author: Christina Roberts <christina@edx.org>
Co-Author: David Baumgold <db@edx.org>
Co-Author: Diana Huang <dkh@edx.org>
Co-Author: Don Mitchell <dmitchell@edx.org>
Co-Author: Julia Hansbrough <julia@edx.org>
Co-Author: Nimisha Asthagiri <nasthagiri@edx.org>
Co-Author: Sarina Canelake <sarina@edx.org>

[LMS-2370]

Fixes: AN-657