Adding ViewFiles extension, v1.0.3.

Adds a [[Special:ViewFiles|special page]] to view the current
contents of a limited set of files.
For more info, see
https://www.mediawiki.org/wiki/Extension:ViewFiles

Change-Id: I9c1361644d5e9c13d340d39fef03744ad6b1bcb5
Merge "Adding ViewFiles extension, v1.0.3."