Add Pills for Mentions & MXIDs in Replies
Most of #189 (closed) has been implemented save for this. When a user is mentioned, this would be not just highlighted, but also have a "pill" with the user's avatar.
In replies we can use pills as a replacement for the MXID, too.
!242 (0a4a4656) can be used as a reference implementation for pills.
- Create pills on mentions
- Replace MXIDs in replies and names in mentions with pills
- Ensure pills look as expected