fixes ios7 button pressed effect

Issue
-
Issue #457 - ios7 button pressed effect not showing up.

Test Case
-
in the kitchensink app, replace the src css files with af.ui.css, and open the app, change to ios7 theme, buttons demo. notice that when you click a button, it does not have pressed effect.

Fix
-
ios7.css: 
- added <code>background: white;</code> in <code>#afui.ios7 .button.pressed</code>
- fixed type for .yellow button

index.html
- changed the css order to match that of af.ui.css, makes debugging easy