Breaks data format: Require one description per @break, add title field

[kfranqueiro]

This makes a couple of changes to help prepare for future goals with regard to documenting breaks.

• Removes the ability to log multiple different break descriptions within a single @break entry
  • I initially included this for convenience, but it only affects a handful of instances (out of around 200), and meanwhile it would add complexity to additional per-break fields such as a title or a fix description
  • Note that the changes related to this will be easier to view with whitespace ignored since it removes a level of indentation in BreaksList.tsx
• Adds title field
  • This is not yet used or populated, but will be useful for W3C's purposes and Rachael suggested it would be useful for Accessible Community's purposes as well
  • .optional() should eventually be remove once title is added for all breaks