(Option to) only show read receipt for the latest read message.

[drasbeck]

Read receipts are awesome, but they also clutter the chats, with too many blue ticks. In the name of simplicity only the latest read message needs to be marked, to know that all messages before it were also read.

I suggest to take note from other services, such as Facebook, and only show a tick by the latest read message. Any messages with the unread status should still retain the light grey tick, indicating that it is not yet read.