Icons in buttons should always be 16px

[atjuan]

The size of the icons on both the single icon and text+icon buttons should always be 16px regardless of the size of the button. So the size of the icon in a btn-sm should be 16px. We are trying to avoid icons less than 16px.

In the future we would like the regular buttons, the 40px height ones, had a larger icon to grow proportionally, but that would involve reviewing the design grid of the icons so now we have to adjust to have a single size of icon for the two sizes of button.