Add ADR for relative courseware dates

[cpennington]

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[ormsbee]

FYI (no action required, but it's likely of interest to you): @davestgermain, @abutterworth, @davidjoy @bradenmacdonald, @symbolist

[ormsbee]

LGTM, though I don't know if you want to add anything extra about rejected alternatives at the end.

[bradenmacdonald]

Are relative due dates only applicable to self-paced courses?

I'm wondering if it makes sense to have an ultimate goal of converting all course dates to relative dates, and deprecating absolute dates entirely. After all, if I run an instructor-paced course in 2019 and then re-run it in 2020, I'll likely want all the due dates in 2020 to be similar (relative to the start date) to the 2019 course. But my understanding from the documentation is that currently the instructor has to go through the course and manually change all the dates to be (new absolute dates that are) relative to the new start date.

[cpennington]

Yes, the goal is to move all courses to relative dates, for exactly the reason you describe. That's a bit further down the pipe, but will be opened up by this work.

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