Provide option to not download media in a room by default. Use blurhash or similar, and only download when the user taps the preview

**Is your feature request related to a problem? Please describe.**
Sometimes you don't want to download all media in a room by default, maybe you are friends with horrible people or are getting a lot of automated media.

**Describe the solution you'd like**
Per-room, there should be a setting to delay downloading media.

**Describe alternatives you've considered**
None, this idea is stolen from WhatsApp