Implement and use new message tracked event

This MR implements a new event that is emitted for all conversation messages that are tracked (incoming and outgoing messages) as discussed in the chat.

The event does only carry information about the timestamp and whether the message was read or not - the information about whether the message is outgoing or incoming was not always available, but is also not needed for the contact list to update.

I hope I updated all places where the conversationManager should be called instead of the messageTracker (i.e. all messages that are possible in private chats). Also, I failed to run the whole test suite in IntelliJ. Is there a special way of running it?