AUI-1321 Button search cancel icon is mispositioned when wrapped inside input-append

Hey @Robert-Frampton,

Here is an update for https://issues.liferay.com/browse/AUI-1321. 

The button search cancel icon is mispostioned because it's missing a font size. The .input-append in Bootstrap 2 has a rule that sets the font size to zero, but the .btn-search-cancel and icon dont have a rule that sets the font property. Thus, the font size is inherited from the .input-append and causes the icon to be mispositioned. My original fix was to set the font size back so that the icon can be positioned correctly. However, I think Eduardo is right. The hardcoded font size seems too fragile. After looking into this a bit more, another way we can fix it is to align the icon in the middle vertically. I have checked that this does not break the gutter attribute since the gutter sets the alignment on the icon's containing div (.btn-search-cancel) not the icon itself. Please let me know if there's any issues. Thanks!