Determine (and possibly tweak) ENS avatar behavior

[mds1]

In https://github.com/ScopeLift/umbra-protocol/pull/296 we added support for ENS avatars. Since they sometimes load slowly, in that PR we decided to show Jazzicons as a placeholder until they load. However, this may be suboptimal UX—see discussion in that PR for more details

Scope of this issue:

• Is there a suggested standard approach/flow that ENS recommends? If so, let's follow that
• If not, decide between:
  1. Keeping the jazzicon > avatar flow
  2. Showing a loading spinner until the avatar loads
  3. Showing a placeholder profile picture until the avatar loads