Remove distinction between recoverable/non-recoverable errors in the AI architecture doc
Added XML handling for student training
Merge pull request #331 from edx/will/ai-grading-arch-revisions-3

AI Grading architecture doc revisions
Merge pull request #326 from edx/will/student-training-xml

Will/student training xml
Student training handles changes to rubric and examples mid-flight.
Silence cache key warnings
Optimize database queries for student training
Merge pull request #333 from edx/will/student-training-in-flight

Student training in-flight changes
Integrate the student training API with the XBlock.
Adding the Student Training UI