Support [[Portal:Skr|Saraiki]] language

It should be noted that [skr] was just approved by the languages committee of the WMF, for creation of Wikipedia at least. For now all Wikimedia projects are still in Incubator.

Here on this wiki, it will remain [skr-Arab] (which is already enabled), even if there are 3 other scripts (including an historic Indic abugida, Multani, which was specifically used for that language; plus Devanagari and Gurmukhi, or Latin transliteration sometimes used today.) This won't block the import and creation of the new Wikimedia wikis (using mainly the Arabic script) as they work already in Incubator: the code [skr] can then remain disabled on Translatewiki.net (and because it was already disabled, there's no need to merge an inexixtant [skr] dataset with the existing [skr-Arab] dataset).