Static assets spring-cleaning

Not needed for Ic0a4a4bdf (JavaScript-powered EventLogging), but since
we're already here we might as well leave it better than we found it:

* Upgraded jQuery from 1.4.2 to 1.9.1. There have been a lot of
  bug-fixes and performance improvements in the intervening time.

* Ran PNGCrush against the PNGs to reduce their file-size.

* Removed a junk .DS_Store file and added a .gitignore file to prevent
  it from reappearing.

* Updated the favicon to match the most recent version used on
  wikimediafoundation.org. It has a higher resolution, making it suitable
  for platforms that have large / hi-res bookmark icons.

* Made a couple of tiny modifications to CollapsibleNav.js to get it to
  pass jshint (namely: add optional radix parameter to parseInt; test
  for strict equality.)

Change-Id: I178e2c9af9819108eed030eb0a56822f31b647a5
Merge "Static assets spring-cleaning"