Fixes BLD-1104
Merge pull request #3962 from edx/dcs/BLD-1104

Fixes BLD-1104
Fix performance regression
Remove course_from_id
don't fetch whole course when the root will do
don't fetch even the root if the id will do
check for definition.data == null
OpaqueKey copy and deepcopy are identity ops
because keys are immutable
pymongo son optimizations
Update to tagged version of pymongo
Use commit hash v tag for pymongo
Fix variable name.
Update hash to latest version.
Merge pull request #3995 from edx/diana/update-req

Diana/update req
Merge pull request #3984 from edx/diana/problem-loc-str

Fix problem_location_str on legacy dash
Fix to excess asset query