SpecialWatchlist: Add an option to automatically reload the page when a filter was...

SpecialWatchlist: Add an option to automatically reload the page when a filter was changed

The biggest negative point (as far as I can tell) with the change mentioned in the follow-up
is, that a user needs at least 3 clicks to change an option, which before it required only
one click. This option adds a new preference for the watchlist (which can be enabled/disabled
using Special:Preferences) which, if enabled, loads a new, tiny module with a script, that
listens on all input and select fields in the header form of Special:Watchlist. Whenever one
of these elements get changed, the watchlist form will be submitted automatically.

The default for this option is false (disabled).

Follow up: I3bcd27596c21aa4

Bug: T50615
Bug: T119322
Change-Id: Icab1a5143df24a06f468165421d40db8fa57e73c