Maintain file order when iterating wikiversions.json

Load wikiversions.json as an ordered dict to preserve php behavior of
iterating the dict in the order that is given in the json file. This
insanity brought to you by the variance of generating ExtensionMessages
with different wikidb versions.

Bug: 63659
Change-Id: I3c5ca78ae624f8027e8dc3c0a13212987edad477