Allow configuration of hero image size in email notifications (or make it user-friendly)

[mfalkvidd]

The hero image introduced in email notifications looks great, but gets in the way of the actual notification content. The "planet-sized" (as one of our users called it) notification forces users to scroll down to see the notification contents, which kind of defeats the purpose of an notification email.

This is what a notification email looks on an iphone:

Our workaround is to manually alter each and every email template. We decided to scale down the image to 30px (10% of the current size).

However, by modifying all email templates we will be stuck on the current version of the templates, since any future update of the default template will be ignored.

I'm adding this feature request in case more nodebb users find the hero image annoying. The solution could be to make the size centrally configurable, or to opt for a default size that is more sensible (with consideration to the goal of email notifications).