Bug 58944 - site.mediawiki_message: support multiple messages

Added site.mediawiki_messages() added to handle request of several messages.

https://bugzilla.wikimedia.org/show_bug.cgi?id=58944

Change-Id: I64710f67c04a0d2b93c70d9edd472f8bab4ce309
Merge "Bug 58944 - site.mediawiki_message: support multiple messages"