Optionally hide previews in notifications

This is a privacy feature offered on mobile and I feel like it's worth considering.

This setting should ignore images and body text sent to the notification server. Images because they can be private information like avatars. Body text should be optional and often contains specific information, message previews, etc.

We should be careful to make sure that the notifications our apps send don't expose sensitive information in their titles.

Critical notifications should ignore this setting