Updated to match Chrome's Setting page a tiny bit better

* Changed default text color to #303942
* Made links have an underline by default, and disabled it where needed
* Made header background slightly transparent
* Increased .content padding-top by 5px
* Changed button:disabled to have cursor: default;
* Fixed the .close-button image. I got the pic from http://goo.gl/JOaN39
* Added a pic for .close-button:hover
Improved the .close-button

Got the pics from chrome://theme/IDR_CLOSE_DIALOG and
chrome://theme/IDR_CLOSE_DIALOG_H
Merge pull request #8 from janka102/tiny-detail-fixes

Updated to match Chrome's Setting page a tiny bit better