Add touch-action: manipulate to .btn

By default on a lot of mobile devices there is a 300ms delay between tapping on a button and the tap being executed, as the system waits to see if the tap is actually a double tap. [More info here](https://developers.google.com/mobile/articles/fast_buttons).

On IE10 (with prefix) and IE11 you can specify the touch behavior by setting the `touch-action` CSS property of an element ([More info](http://msdn.microsoft.com/en-us/library/windows/apps/Hh767313.aspx)).

This change adds `touch-action: manipulate` to the .btn class, effectively disabling double tap on buttons that use that class and thereby removing the 300ms delay when tapping those buttons in IE10+.