(bug #56685) Parsing of localized quantities.

This introduces MediaWikiNumberUnlocalizer which relies on
MediaWiki's Language class for converting numbers to canonical form.

IMPORTANT: requires I9acb56d4f7f4 to be merged. (done)

Change-Id: I996e8d032a476d245bbfc2872d7eae4bbad79cb1
Merge "(bug #56685) Parsing of localized quantities."