Explicit plural support for 'echo-overlay-title-overflow'

Requested by Skalman at
https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Echo-overlay-title-overflow/sv

Change-Id: Ic17d613a9653c7d7671c5232ac90ecd52b2a11e0
Merge "Explicit plural support for 'echo-overlay-title-overflow'"