Extend and implement user preferences to allow users to customize how their recent changes feed is dealing with updates from external pages, e.g. Wikidata.

Added a filter for Wikidata changes in https://gerrit.wikimedia.org/r/#/c/34285/

Do we still need a separate user preference for that or is the filter for show/hide Wikidata entries enough?

Follow up for the preference https://gerrit.wikimedia.org/r/#/c/34325/ The preference is important to have.

It's merged.

Verified in Wikidata demo sprint 24

I seem to be running into a problem with this trying to load http://test2.wikipedia.org/wiki/Special:RecentChanges which I have reported:
http://meta.wikimedia.org/wiki/Talk:Wikimedia_maintenance_notice#Recent_Changes_on_test2.wikipedia.org_is_broken

Invalid option hidewikidata
Backtrace:
#0 /usr/local/apache/common-local/php-1.21wmf6/includes/FormOptions.php(150): FormOptions->validateName('hidewikidata', true)
#1 /usr/local/apache/common-local/php-1.21wmf6/extensions/Wikibase/client/WikibaseClient.hooks.php(379): FormOptions->getValue('hidewikidata')
#2 [internal function]: Wikibase\ClientHooks::onSpecialRecentChangesQuery(Array, Array, Array, Object(FormOptions), Array, Array)
#3 /usr/local/apache/common-local/php-1.21wmf6/includes/Hooks.php(255): call_user_func_array('\Wikibase\Clien...', Array)
#4 /usr/local/apache/common-local/php-1.21wmf6/includes/GlobalFunctions.php(3852): Hooks::run('SpecialRecentCh...', Array)
#5 /usr/local/apache/common-local/php-1.21wmf6/includes/specials/SpecialRecentchanges.php(409): wfRunHooks('SpecialRecentCh...', Array)
#6 /usr/local/apache/common-local/php-1.21wmf6/includes/specials/SpecialRecentchanges.php(157): SpecialRecentChanges->doMainQuery(Array, Object(FormOptions))
#7 /usr/local/apache/common-local/php-1.21wmf6/includes/SpecialPage.php(613): SpecialRecentChanges->execute(NULL)
#8 /usr/local/apache/common-local/php-1.21wmf6/includes/SpecialPageFactory.php(501): SpecialPage->run(NULL)
#9 /usr/local/apache/common-local/php-1.21wmf6/includes/Wiki.php(291): SpecialPageFactory::executePath(Object(Title), Object(RequestContext))
#10 /usr/local/apache/common-local/php-1.21wmf6/includes/Wiki.php(555): MediaWiki->performRequest()
#11 /usr/local/apache/common-local/php-1.21wmf6/includes/Wiki.php(448): MediaWiki->main()
#12 /usr/local/apache/common-local/php-1.21wmf6/index.php(59): MediaWiki->run()
#13 /usr/local/apache/common-local/live-1.5/index.php(3): require('/usr/local/apac...')
#14 {main}