Button Group component enhancements

[DHedgecock]

Add customization and prop enhancements to the ButtonGroup:

• Add ability to switch between button and input[type="radio"] nodes for accessibility and semantics (especially when in forms)
• Add ability to pass the color to the ButtonGroup container instead of each individual ButtonGroup.Button
• Enable overriding generated theme colors with a map
• Add borders options (preferably w/ a border around container and single borders on buttons to prevent verbose css)
• Add ability to include btn style dropdowns inside button groups by targeting .dropdown-trigger button class.