Do not bold all entries of an unvisited page on the Watchlist

When a page is unvisited (wl_notificationtimestamp IS NOT NULL) all
entries of that page on the watchlist gets bold (class=mw-changeslist-line-watched),
because wl_notificationtimestamp is only checked for null.

wl_notificationtimestamp should be compared against rc_timestamp to
find only the really unvisited pages since the last visit on that page.

It is confusing, when all entries of a page on the watchlist gets bold,
but only some of the newer are unvisited.

Support for old and enhanced watchlist.

Change-Id: I7265141a6c84bcbdd7b651bd2983a08b73c6ddfe