Set mw.config wgFileExtensions only on Upload instead of site-wide

It is just used by mediawiki.special.upload

Change-Id: I433e29866fe184ba80c5dda35722e228e79f9307
Make TitleMethodsTest a LangTestCase

With I40a51c14ce07c301c15c6c2128cc18bb12e71103 a compare of namespaces
was added which fails when content language is not en.

Change-Id: I21466231e10e6cd5969c8c9bfd4824bf9c47e6d8
Merge "Make TitleMethodsTest a LangTestCase"
Merge "Set mw.config wgFileExtensions only on Upload instead of site-wide"
Localisation updates from https://translatewiki.net.

Change-Id: I5d944ab07707d9a1a886ff6336f8136f9fa237ca