with code to translate between addressing schemes based on app
and persistence layer addressing scheme specification.

STUD-1206

LMS-1744

Adds xblock handler_url support to the LMS, and makes handle_ajax use
that code.

[LMS-230] [LMS-229]

Instead, we use XModule field default values when creating an empty
XModule. Driven by this use case, we also allow for XModules to be
created in memory without being persisted to the database at all. This
necessitates a change to the Modulestore api, replacing clone_item with
create_draft and save_xmodule.

Rename fields in CourseTaskLog, including a task_key column for indexing.  Use 'rescore' instead of 'regrade'.  Clean up task submission.

Add tracking calls to reset (and delete).  Add tests for delete.  Remove sleep statement used for manual testing.

Add unit tests for regrading at courseware level (task and task_queue).