Course re-run section and refs to it in others

@explorerleslie, @talbs please check for accuracy and completeness
@WatsonEmily please circulate to PMs for level of detail, other likely questions to address, format
@mhoeber , @srpearce please consider this a developmental/copy edit
@sarina, @nasthagiri if you have time I value your input also!

confirmed. the only date that we change is the course start date, to override all other dates and make the course not go live as soon as the course is re-run. Every other section and subsection release/due date must be changed by the course team from the course outline.