Fixed issues with Background transparency 

This is to fix issue related to transparency of the navbar background.

Issue 1:
When you set the transparency to 0, the CSS property disapear from CSS inline. This is due, to the value returning NULL, so I added a conditional statement to fix this

Issue 2:
The transparency was not working to IE8, so I added a filter that makes it to work crossbrowser, even to older versions of IE
Merge pull request #350 from griiettner/master

Fixed issues with Background transparency