chatview: messages should not be displayed one by one
Currently messages are displayed one by one when loading a conversation.
Why ? The user shouldn't wait too long for messages to appear on screen. This might be the case if we load a large conversation in one single batch.
However, for small to medium conversations displaying messages one by one is a terrible perfs bottleneck because it triggers a large number of expensive DOM updates/redisplay.
Fix: Load conversations in one single batch and implement lazy loading at the same time. That way we have the advantages of batch-loading without the drawbacks.