Story 487: Footer update

* Last modified is a link pointing to page history (text is also the
  same size as footer text).
* About and Disclaimers links removed.
* "Page by contributors like you" removed.
* Footer markup simplified, CSS redone.
* logo-copyright-en.png cropped (removed a bit of white background) to
  avoid using vertical-align for centering.

Change-Id: Ifd6dff45b7931348db60abed76952d74d7947db4
Merge "Story 487: Footer update"