Make mwe-upwiz-license-external* more grammar friendly and clearer

By making the source site name into a quotation, we should
avoid some problems with declension. Suggested by Siebrand.
<https://translatewiki.net/wiki/Thread:Support/About_MediaWiki:Mwe-upwiz-license-external-invalid/ksh>

Also replaced "not appropriate", per MarkTraceur.

Change-Id: I14a988e705c4be7d7eeab2072e03a78e0a8324d4
Merge "Make mwe-upwiz-license-external* more grammar friendly and clearer"