Clear children cache when binding an XBlock to a user.

Update social media links in EdX footer.

Make XModule use the same get_children that XModuleDescriptor and XBlock do, and make it returned the same CombinedSystem

Prior to this change, if a CachingDescriptorSystem was prepopulated
with XBlock field data (`module_data`), then it would be used as
the DescriptorSystem for blocks loaded through it. On the other hand,
if it had to fetch new data from the modulestore, then a new
CachingDescriptorSystem would be created by the modulestore, and used
by the newly returned object.

This commit allows the modulestore get_item and get_items methods
to accept an existing CachingDescriptorSystem to augment with data
from the backing mongo store, and to use as the DescriptorSystem
for newly loaded XBlocks.

Reduce queries from FieldDataCache

Replaces some PLATFORM_* settings with a more
general setting for specifying social media
URLs in the footer.

Adds icons and titles for new social media
sites (Tumblr, Reddit, Youtube) to match
EdX.org.

Remove unused imports

Fix test_instructor_dashboard.py tests

Implement full preferences API

TNL-1493

See https://openedx.atlassian.net/wiki/display/TNL/User+API for details

This file was never run, because of a missing __init__.py.  It needs a
super() call to make the ModuleStoreTestCase work properly.

Then one test failed, because of a missed change from dollar to
configurable currency.

Update the bok-choy version being used. TE-783

Simple capitalization fix

Remove old env settings files

pass opts From PythonTestSuite to NoseTestSuite

Instead of referencing the example externally, we now explain the
setting inline.

This contains hard-coded reference to out-dated courses.

This looks to have been a personal configuration file.

Is this used? It contains MITx references.

These all date back to 2012 and are hard-coded for specific course runs.

Define TENDER_SUBDOMAIN so that we can still use vanity URLs

Update translations (autogenerated message)

Revert "To support UNICODE xblock.location"