Insert css styles for badges on client

Creates css styles for classes in for all badges specified in the new
"displayBadges" setting. The setting must be an array of serialized item
ids pointing to the class name.

In wikibase.client.css the actual icons are specified which can however
still be overwritten in the wiki's Common.css pages. The currently
supported names are "wb-badge-goodarticle" and "wb-badge-featuredarticle".
The icons used are [1] and [2]. Both images are licensed under public domain
because they consist entirely of information that is common property and
contain no original authorship.

[1] https://commons.wikimedia.org/wiki/File:Monobook-bullet-star-gray.png
[2] https://commons.wikimedia.org/wiki/File:Monobook-bullet-star-transparent.png

Bug: 60717
Change-Id: I818dbb3433b6618c4e1967018765d44f02e9970c
Merge "Insert css styles for badges on client"