Add dataset

[paylakatel]

This PR:

• adds the ability to view fatality data - gives users to see either the fatality data or crash data (not at the same time)
• makes sure users can filter the fatality data by mode type and date
• changes the default date calculation to leverage date-fns and sets it back more months to future proof ourselves
• adds placeholder links for finding the fatality data and placeholder text for explaining it (waiting on final approval and posting)