Accordion V2

[maxatdetroit]

Part of #202 & #205

This PR does the following:

• Simplifies attribute naming conventions (removes data- prefix)
• Migrates to using slots with basic markup
  • Removes the cod-accordion-header and cod-accordion-body components since they are unnecessary
  • Keeps the cod-accordion-item because it is necessary to set the id of nested accordion items programmatically and provide a container for styling
• Temporarily removes support for list-style (example on dev storybook)
  • This will be added back in a separate PR. The implementation is so different that it'll be easier to review as a separate PR.
• Permanently removes support for custom styling (example on dev storybook)