[Update] Button Group

[travis-spanu-nearform]

Note: Most of the color changes should be inherited the token changes made for the button component

• Hover state changed from black to darker shade of primary
• Focus changed from black to primary default
• Colored dropshadow added to focus state
• Dark mode: Primary button group changed from white to light blue.

P.S. We had separated components for vertical and horizontal button groups but I combined those and made orientation a property of a single button group component.