Spike: can we link to courses & assignments in each of the major LMS's

This question will have to be answered separately for each LMS that we care about, for example: Canvas, Blackboard Classic, Blackboard Ultra, D2L, ...

Do assignments actually have their own URLs? And can Hypothesis actually get or generate the URLs for assignments?

It has been [clarified in Slack](https://hypothes-is.slack.com/archives/C04J58NGMC4/p1674062778526299) that we do still think that the email notifications feature is worth implementing even if we can't link to assignments at all. Linking to assignments is just a nice-to-have.

Slack threads:

* [Can we get assignment URLs from LTI variables?](https://hypothes-is.slack.com/archives/C04J58NGMC4/p1673284075660749)
* [Linking to Blackboard assignments](https://hypothes-is.slack.com/archives/C04J58NGMC4/p1673968399731459). Contact with [Blackboard support about linking to Blackboard assignments](https://hypothes-is.slack.com/archives/C04J58NGMC4/p1674245491621139)
* [Linking to Canvas assignments](https://hypothes-is.slack.com/archives/C04J58NGMC4/p1673968513420429)
* [Linking to D2L Brightspace assignments](https://hypothes-is.slack.com/archives/C04J58NGMC4/p1673968632016649)

An alternative to linking directly to assignments within LMS's might be to [implement launching Hypothesis assignments outside of LMS's](https://hypothes-is.slack.com/archives/C1MA4E9B9/p1674064452108179).

# Fallback solutions

If we can't link directly to the assignment then if possible we should do one of these:

* Link to the assignments section within the course (e.g. link to the "folder" containing the assignment in Blackboard)
* Link to the assignment's course
* Link to some sort of useful page within the LMS instance where the user can see their assignments or course, e.g. some sort of user profile page
* Link to the front page of the LMS instance