Add button group styles for radio buttons

[ryanleichty]

We often use radio groups over drop down menus for the improved UX when you have few items to select from. It would be amazing if you could alternatively display the radio buttons as a button group with text only, icon only (using the font awesome library), or both.

It's kind of similar to this #15804 in that it's providing an alternative UI for the same kind of input.

I know some third party plugins exist for this, but it would be great if this were natively supported.

[daltonrooney]

I agree, this would be a nice improvement. I would also love an option to align the default radio field vertically or horizontally. Sometimes a horizontal radio list is a better use of space.