the messages in a thread were previously rerendered every minutes to
update their timestamps. This commit only update the timestamps, not
all the message. This will allow us to keep expanded/folded state in
messages without collapsing them every minutes.
[IMP] mail: add read more/read less support client side
Messages are cleaned up and tagged server sides, with a attribute
data-o-mail-quote. This commit replace their content with a clickable
read more link, which toggle its display.