Changing code to follow MediaWiki coding conventions

No functional or display changes in this commit.

Changes include:
- Remove quotes from url()s, as they are not needed
- Opening braces for CSS declaration block on the same line as the (last) selector
- Indent each declaration with a tab
- An empty line between one CSS rule set and the next

Other changes in the commit include:
- Change image resources to use shorter Wikia image URL method

Full MediaWiki coding conventions used are available at:
- http://www.mediawiki.org/wiki/CC
- http://www.mediawiki.org/wiki/CC/CSS