Style Flag Button When Icon Only is Selected

[mrjarbenne]

When Jetpack Sharing is enabled, we have already adjusted the CSS to some degree so the button works within that array of buttons; but the Sharing settings allow you to configure the icons to appear as Icons Only:

When that's selected, the flag button needs to be adjusted:

[r-a-y]

Done. I've also added support for the 'Text only' option as well.