(bug 36002) Configure $wgMobileUrlTemplate for sourceswiki

Configuring $wgMobileUrlTemplate for multilingual Wikisource
('oldwikisource') the way it's configured for foundationwiki.
Please note that even though the link will look nice & dandy,
the mobile view still won't work per bug 29364.

Bug: 36002
Change-Id: Ide7d1e2f387dce6345af24fd44e8bdb19b25dcec