made glyphicon hidden text the same size as the glyphicon

This is primarily an issue with VoiceOver and ChromeVox since they draw an onscreen focus when browsing the DOM.

The "hidden" text is now hidden on screen, and it's the same size as the glyphicon and in the same position as the glyphicon. This makes the onscreen focus while running a screen reader better. When the hidden text is off screen, screen readers like VoiceOver and ChromeVox will draw their screen reader focus off of the screen. By placing the hidden text over top of the glyphicon the screen reader visual focus displays more accurately.