Button group: documentation and component updates

[Spark450]

Acceptance Criteria:

• Change the default alignment of the button group to "left"
• Chain icon size displayed in the sandbox (and the corresponding code) with the selection of gap (Discuss)
  • compact gap, show "compact buttons"
• Undocument the "Align - centre" property option
• Add ability to set number of buttons in the button group (from 1-4 buttons)
• Add icon button variant
  • Boolean "Icon only" (checkbox)
  • icon buttons, show the icon button group with "compact" gap (Discuss)