#229 Click to highlight a message

[Victor Porton]

Make the following thing when a user clicks poster name in the left sidebar:

The last clicked message should be emphasized with a different background color.

This may help to track the read messages, for example, the clicked and emphasized message may be the last read (or first unread, dependently on user's taste) message. This is very useful to track which messages are already read and which are yet to be read.