ChatPage: Group messages from same author

A message group has only one avatar (displayed next to the first
message) and messages from the message group have smaller spacing.
3 jobs for master in 2 minutes and 56 seconds (queued for 115 minutes and 42 seconds)
Status Name Job ID Coverage
  Test
passed build #129702

00:01:03

passed clazy #129700

00:01:24

passed qmllint #129701

00:00:27