Don't show cohort information when disabled

TNL-552
Address code review comments
Minor cleanups
Performance enhancements for unit tests
in test_contentstore, don't load the xml course if not necessary
Upgrade pymongo
LMS-11437
Test multiple threads linear growth
Remove unused credentials from mongo init
was breaking pymongo 2.7
tz aware
Merge pull request #5501 from edx/andya/disable-cohorts-ui-bug

Don't show cohort information when disabled
Small changes to the segment.io event handler
Updates 10-7 release notes
Merge pull request #5537 from edx/sylvia/docs/relnotes10-7

Updates 10-7 release notes
Merge pull request #5527 from mulby/tweak-segment-io-endpoint

Small changes to the segment.io event handler
Make unit tests work on older mongo versions
Consistently ensure dog_stats_api tags are formatted correctly
Added handling in gitlog for missing import logs

Fixes a template error that occurs when viewing a course's detailed
git import log. The problem happens for courses imported using methods
other than the `git_add_course` command.
Merge pull request #5288 from edx/split/info_perf

Upgrade pymongo
Merge pull request #5431 from open-craft/datadog-wrapper

Consistently wrap the DataDog API to prevent logged errors & missing stats data
Merge pull request #5423 from mitocw/bdero/fix-gitlog-focused-error

Added handling in gitlog template for missing import logs
Dont' need error check call in old mongo on this test