Consolidate information from data.edx.org, Appendix E, and problem types
Merge pull request #2943 from edx/sylvia/documentation/BLD-850

Consolidate information from data.edx.org, Appendix E, and problem types
Edits from Alison's initial review

DOC-34
Merge pull request #2947 from edx/markhoeber/documentation/doc-34

Edits from Alison's initial review
Initial implementation for system_manager app
Tightened up session impl
Removed unnecessary imports
Resolved merge conflicts
Added resource URIs and documentation reference
Added test harness for API calls
Added placeholder tests and fixed a couple bugs
Added EDX_API_KEY support
Added groups
Added support for creating/retrieving users.
Added delete/inactivate workflow for users