Is your feature request related to a problem? Please describe.

In channels / group chats, avatar placeholders are displayed in gray. This may make it hard to read message history, for example if two people are talking, and one of whom has a nick that starts with 'n' while the other has a nick that starts with 'm'

Describe the solution you'd like

Implement XEP-0392: Consistent Color Generation for avatar placeholder colors. The XEP will assure consistency with the avatar placeholder colors shown in other clients.