Web: revise navigation bars with CSS gradients (issue 193140043 by address@hidden)

[paulwmorris]

Reviewers: ,

Message:
Please review. A demo showing the desired result can be found here:

http://clairnote.org / lilypond-web-demo2/

(just remove the two spaces in the url)

Things should look the same in IE8 and IE9 as in other browsers.

I will also need to add some images to the lilypond-extras repo that go
with this revision.  These are the Lily icon used in the LilyPond
("home") tab:

  lily-home-32x32.png

and these gradient images used as fallbacks for IE9 and lower:

  nav1-bg.png
  nav1-hover.png
  nav1-active.png
  nav2-bg.png
  nav2-hover.png
  nav2-active.png

Description:
Web: revise navigation bars with CSS gradients

Includes background image fallbacks for IE9 and
lower in separate, conditional CSS file.

Please review this at https://codereview.appspot.com/193140043/

Affected files (+86, -137 lines):
  M Documentation/css/lilypond-website.css
  M Documentation/css/lilypond-website-ie-fixes.css
  M Documentation/lilypond-texi2html.init