Fix delete messages in course outline
STUD-2019
Reduce calls to expensive methods in create_xblock_info

Special-case the outline page requests.

STUD-1997
Merge pull request #4604 from edx/dan-f/improve_outline_performance-2

Reduce calls to expensive methods in create_xblock_info
Merge pull request #4601 from edx/benmcmorran/delete-message

Fix delete messages in course outline
Reduce parent/child lookups in create_xblock_info

STUD-1997
Merge pull request #4614 from edx/dan-f/improve_outline_performance-2

Further performance improvements to course outline
Edit section/subsection release dates and grading types.

Fix bok_choy test by changing course separator.
Change format of the modal title to '[Subsection/Section Name] Settings'.
Improve bok_choy test stability.
Studio: correcting modal window size name for outline settings editor
Specify full date in bok_choy tests.
Refactor bok_choy tests.
Remove .modal-editor from basic-modal.underscore
Set classes in modal window dynamically.
Studio: revising outline edit modal tip content and overall size
Rename isEditable to isEditableOnCourseOutline.
Interpolate display name.
Use graded instead of format as flag.
Studio: revising outline settings edit modal size
Fix selectors in bok_choy tests.
Merge pull request #4425 from edx/alex/edit_course_outline

Edit section and subsection at course outline page.
Remove code and template responsible for subsection edit page