Rename Studio logo

OPEN-301
add logging for cybersource errors; fix minor unicode bug
Add a `created` field to OrderItem.
Remove multi-threading test as unnecessary and flakey
also fix other users of check_mongo_calls to use None if they don't care about sends
PLAT-239
Merge pull request #5868 from edx/diana/add-created-to-orderitem

Add a `created_at` field to OrderItem.
Merge pull request #5871 from edx/dhm/remove_test

Remove multi-threading test as unnecessary and flakey
Merge pull request #5841 from edx/cms-consistent-branding-image-names

Rename Studio logo
Merge pull request #5869 from edx/adam/unicode-fix

add logging for cybersource errors; fix minor unicode bug
Display validation messages for any xblock on the container page.

TNL-683
Studio: revising element-level xblock information styling
Studio: revising xblock validation message list styling
Merge pull request #5710 from edx/christina/general-component-errors

Support validation messages for any xblock (on container page).
Merge pull request #5873 from edx/release

Release