- Ensure that only a course import is saved to the draft branch and then
published. A content library has only a single 'library' branch.
- Add a fields parameter to the create_library call so the call has the
correct number of parameters.
- Add tests which import content libraries using different test methods
and with different branch settings.
- Add test which imports a content library and then exports it.
- Use XBlock module version that supports XML-serialized String of None.
- Add re-import of content library and equality comparison to test.
- Allow get_items to be called on LibraryLocators.

Fixes test failures in e4613749

This reverts commit acf6c1d6, reversing
changes made to c59db6e5.

for use when a test class has a setUpTestData() method which uses
variables set up in the setUpClass() method.
Change base teams API test class to use the context manager.

This now correctly migrates and dumps files for both databases.

Run lettuce migrations for both databases

This abstract class contains most of the fields (aside from the id and
foreign key to StudentModule that the subclasses need to manage).  It
also provides a get_history method that abstracts searching across
multiple backends.

Move router code to openedx/core
We need to use it from cms and lms.
Ensure aws_migrate can be used for migrating both the lms and cms.

Handle queries directed to student_module_history vs default and the
extra queries generated by Django 1.8 (SAVEPOINTS, etc).

Additionally, flag testing classes as multi_db so that Django will
flush the non-default database between unit tests.

Further decouple the foreignkey relation between csm and csmhe

When calling StudentModule().delete() Django will try to delete CSMHE
objects, but naively does so in the database, not by consulting the
database router.

Instead, we disable django cascading deletes and listen for post_delete
signals and clean up CSMHE by hand.

Add feature flags for CSMHE
One to turn it on/off so we can control the deploy.
The other will control whether or not we read from two database tables
or one when searching.

Update tests to explicitly use this get_history method rather than
looking directly into StudentModuleHistory or
StudentModuleHistoryExtended.

Inform lettuce to avoid the coursewarehistoryextended app

Otherwise it fails when it can't find features/ in that app.

Add Pg support, this is not tested automatically.

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

By default, migrations are applied as they always have been. Exporting DISABLE_MIGRATIONS=1 or passing --disable-migrations to Paver commands will create tables directly from apps' models.

TNL-4151 had previously been fixed to avoid a flaky condition; however,
that only passed the flaky condition to a later point in the
test. The proper fix is to ensure the page has loaded. Putting the
definition in this method will mean that the page will wait
to load with other functions, such as `DashboardPage.visit()`.

When capa problem rendering was moved to happen inline on courseware
page loads, we started executing many more Mako templates on sequences
with large numbers of thse problems. To help offset this, we're caching
the context generation (it showed up as the easiest piece of low
hanging fruit on profiles of the courseware index page).

[PERF-261]

Before this commit, calling the student_view on a capa problem would
cause it to render an empty placeholder <div>, wait for the
DOMContentLoaded event to be fired, and then make AJAX requests to the
the problem_get handlers to retrieve the HTML it needed to render the
actual problems. This can significantly increase the end user load
times for pages, particularly when there are many problems in a
vertical.

This commit takes a very conservative approach and has the server side
add the rendered HTML into a new data-content attribute on the <div>
enclosing the problem. When Capa's JS initialization runs, it grabs
from that data-content attribute rather than reaching over the network
for an AJAX request.

I had attempted to make it somewhat smarter and push the rendered
problem straight into the document instead of relying on the
data-content attribute. This was faster, and should be our long term
goal. However, it caused odd bugs, particularly around MathJAX
rendering, and I never quite tracked the issue down. I'm still going
forward with these changes because it's significantly better than the
current situation that students have to deal with, and we can make the
JS more performant in a future iteration.

[PERF-261]

Delegating the conditional to the has_configuration_Set method, which is overriden by the database backend, so the enable_pre_startup works well for both backends.

Adding tests

Fix quality issues

The get_or_create function is vulnerable to race conditions in MySQL, which can
cause the model LoginFailure to, in some cases, have more than one row for the
same user, breaking the login for that user.

Addinf functionality to expect and clean the error by deleting extra rows (by
oldest lockout date), leaving just one entry and allowing the user to login.

Replayed and squashed by @efischer19, initially commited by @laq

mathjax preview should be inline by default