Set site logo in mediawiki.skinning.interface module instead of inline styles

Requires skins use the 'mw-wiki-logo' class on the logo element for the styles
to apply and to load the 'mediawiki.skinning.interface' module (or implement
their own skin module that uses the ResourceLoaderSkinModule class).

This is backwards compatible with skins using inline styles as the class only
applies when used.

Bug: 56257
Change-Id: I4e6db89a688843ac24539f8fd1b408c0d04881b3