Parse 'upload_source_url' message on SpecialUpload

Commons wants to use wikitext over there:
https://commons.wikimedia.org/wiki/MediaWiki:Upload_source_url

Change-Id: I7625fb58388de901b93744aa6d21de433f671483
Merge "Parse 'upload_source_url' message on SpecialUpload" into wmf/1.25wmf6