Better differentiate instructor email digests from marketing emails

[seanh]

We're concerned that users may not notice the distinction between marketing emails sent by Hypothesis and the "instructor email digests" that the LMS app sends to notify instructors of student annotation activity in their assignments. As a low-effort way to address this we'd like to:

1. Make some changes to the body text of the instructor email digests. Two possible changes were suggested:

   1. Add some text to the footers of the emails (where the email preferences and unsubscribe links are) explaining that this is not a marketing email but a "transactional" email that you're receiving because of student activity in your assignments. ("Transactional" might be a confusing word for users, brings to mind financial transactions to me, maybe "notification" or "activity notification" is better -- @seanh)
   2. Change the title at the top of the email body from the generic and not very useful There has been some activity in Hypothesis (which is maybe mistakeable for a marketing email) to something more specific like 12 students made 78 new annotations in 3 courses.

2. Make some changes to the LMS app's email preferences page to make it more clear that this is a preferences page for transactional/notification emails only, so that users won't expect it to also unsubscribe them from marketing emails.

   In particular, there was a suggestion to change the title at the top of the page from Email Notifications to something more specific like Activity Notifications.

Here's what the email digests currently look like (you can preview it at https://lms.hypothes.is/admin/email):

And here's what the email preferences page currently looks like:

[jaredpdesigns]

Added a few explorations here

Main suggestions:

• On the standalone preference page:
  • Adjust the title to be "Activity Notifications".
  • Combine the two leading paragraphs to: "Select the days you’d like to receive emails about student annotation activity. This is a useful way to monitor participation."—the suggestion as to why they should care about these might be helpful.
• On the email itself:
  • Change title to "Latest Student Participation in Hypothesis"
  • Differentiate structure of email by bulleting assignment details and bolding numeric values, making it easier to scan.
  • In footer add bolded paragraph: "You are receiving these emails to assist in monitoring student participation within courses"
  • Change links to standalone page to be "Change the frequency of activity updates" and "unsubscribe from all updates" to better distinguish these aren't just emails but updates.