Show flow events in watchlist

Flow events were not showing up in the watchlist due to the need to adjust a query
issued by Special:Watchlist.  A new hook to effect this change has been merged to
master and this updates Flow to utilize it (and hence, enable watchlists).

Bug: 55597
Change-Id: I2ca72fac0153f046b2cb0f94dbc55f2fff3adf7c
Merge "Show flow events in watchlist"