Method to identify if a ChangesList is watchlist or normal

There are differences, like grouping, between watchlist and
normal rendering that hook recipients need to know about.
This exposes if the setWatchlistDivs method has been called
which currently happens immediatly after instantiation in
SpecialWatchlist

Change-Id: Ibc06c6d9b878cad3f5da92cfbe3f650ad3f63efa
Merge "Method to identify if a ChangesList is watchlist or normal"