(bug 25946) The message on the top of Special:RecentChanges is now displayed in user...

(bug 25946) The message on the top of Special:RecentChanges is now displayed in user language instead of content language

Moved 'recentchangestext' message to 'recentchanges-summary'; left 'recentchangestext' empty by default for wikis that would like to display things in content language on the top of Special:RecentChanges

This a resubmit of r86186 (https://www.mediawiki.org/wiki/Special:Code/MediaWiki/86186) which was reverted in r86294 (https://www.mediawiki.org/wiki/Special:Code/MediaWiki/86294). The revert should have been temporary (at least from commit summary), but it seems that it was not the case.

Change-Id: Ia2061a581f754aa1bc374a615d41e8465996feac