fix git_export tests
Merge pull request #6238 from edx/clytwynec/fix_failing_git_export_tests

fix git_export tests
Make a generic django field for storing OpaqueKey classes
Extract common base functionality for storing xblock fields in the relation db
Move lms.lib.xblock into lms.djangoapps.lms_xblock in preparation add database backed configuration to it
Add a configuration model for managing XBlockAsides
Mock out the underlying segment-io call.

TE-532
Teach LMS how to render XBlockAsides

[PLAT-217]
Make ErrorDescriptor more resistent to errors
Merge pull request #6162 from cpennington/xblock-asides

XBlockAsides in LMS
Fix another analytics.init secret error message (noise).
Pipe analytics client output to stdout instead of devnull.
change the context_processor in the shopping cart to return a pointer to a function so that only the templates that actually need to know if the shopping cart button should be shown will actually make the database roundtrips
Merge pull request #6242 from edx/cdodge/move-shoppingcart-button-detection

change the context_processor in the shopping cart to return a pointer to...
set position to default value if POST request don't have position argument
TNL-922
Merge pull request #6210 from edx/zub/bugfix/tnl-922-key-error-getting-position

set position to default value if POST request don't have position argume...
Add header row to email opt in list; add default date
fix preview link generation for course reruns (PLAT-336)
Merge pull request #6233 from edx/adam/fix-preview-courseruns

fix preview link generation for course reruns (PLAT-336)
Merge pull request #6245 from edx/will/email-opt-in-updates

Add header row to email opt in list; add default date