Clean up assets page notifications

Remove hack to work around multiple notification click issues -- and actually resolve
the issue so that the hack isn't necessary

Fix test_system looking like a test to nosetest. Fix class inheritance causing double counting of coverage.

Instrument sequentials with segment-io

Refactor Backbone notifications

pep8 changes made during long refactoring

Fix a bug in diff-cover

Feature/brian/regrade celery 2

Conflicts:
	AUTHORS
	common/lib/xmodule/xmodule/tests/test_annotatable_module.py
	common/lib/xmodule/xmodule/tests/test_capa_module.py
	common/lib/xmodule/xmodule/tests/test_combined_open_ended.py
	common/lib/xmodule/xmodule/tests/test_conditional.py
	common/lib/xmodule/xmodule/tests/test_html_module.py
	common/lib/xmodule/xmodule/tests/test_progress.py
	common/lib/xmodule/xmodule/tests/test_xml_module.py
	lms/djangoapps/courseware/tests/__init__.py

Cherry pick change to url matching regular expression. Fixes LMS-37

remove assets.js from the PIPELINE_JS since it seems to cause that file ...

When changing variable names for code review critique, accidental cut/paste prevented intended behavior.

Fix a few remaining tz naive dates

need to import os

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