Mouseover explanations for interlanguage links in native language

Adds a language name in User's language from CLDR
to an interwiki 'title' attribute. Believed to be
RTL-compilant.

New message added: tooltip-iwiki, added to $preloadedMessages

Bug: 5231
Change-Id: I3dcb00cdc28a10711b6703fa509b8b8d06e325a2
Merge "Mouseover explanations for interlanguage links in native language"