feat(@clayui/button): add api for stacking button group vertically

Author: bryceosterhaus

packages/clay-button/src/Group.tsx

@@ -12,18 +12,27 @@ export interface IButtonGroupProps
 	 * Flag to indicate the spacing between the buttons.
 	 */
 	spaced?: boolean;
+
+	/**
+	 * Flag to indicate if buttons are stacked vertically.
+	 */
+	vertical?: boolean;
 }
 
 const ClayButtonGroup: React.FunctionComponent<IButtonGroupProps> = ({
 	children,
 	className,
 	role = 'group',
 	spaced,
+	vertical,
 	...otherProps
 }: IButtonGroupProps) => (
 	<div
 		{...otherProps}
-		className={classNames(className, 'btn-group')}
+		className={classNames(
+			className,
+			vertical ? 'btn-group-vertical' : 'btn-group'
+		)}
 		role={role}
 	>
 		{spaced

packages/clay-button/stories/index.tsx

@@ -45,6 +45,15 @@ storiesOf('Components|ClayButton', module)
 			<ClayButton>{'group.'}</ClayButton>
 		</ClayButton.Group>
 	))
+	.add('button group vertical', () => (
+		<ClayButton.Group spaced={boolean('Spaced', false) as false} vertical>
+			<ClayButton>{'This'}</ClayButton>
+			<ClayButton displayType="secondary">{'is'}</ClayButton>
+			<ClayButton>{'a'}</ClayButton>
+			<ClayButton displayType="secondary">{'button'}</ClayButton>
+			<ClayButton>{'group.'}</ClayButton>
+		</ClayButton.Group>
+	))
 	.add('ButtonWithIcon', () => (
 		<>
 			<ClayButtonWithIcon