MEDIUM: stats: use multi-line tips to display detailed counters

MEDIUM: stats: use multi-line tips to display detailed counters

Frontend, listener, server and backend detailed counters are now spread
over several lines in a table when the pointer hovers over the <u> area.

The values are much more readble, and the extra space gained this way
allowed to report some percentages.

Note: some incoherencies still exist between some counters. For example,
the backend's cum_conn is increased when a session is assigned instead
of increasing cum_sess.