Handle Miscellaneous ToDos in Script #290

We've a number of miscellaneous todo's in the script. Just to make sure we don't lose track of them, let's catalogue them here and then create sub-issues or reject them as need be.

src/main.css

• Move to design-system, so it can be used elsewhere
• decouple heading styling from heading level in design-system (or at least provide classes that can perform these overrides more efficiently)

vite.config.js

• remove this nonsense and set up in tags at the page level instead.

src/util/dateFormatters.js

• update this util to use date-fns

CONTRIBUTING.md

• make table of core dependencies, and documentation.

src/pages/donate.vue

• uncomment this when we figure out how to get donorbox data into the browser because they do not have a solution for this 🙄

src/api/auth.js

• API should require auth

src/pages/data-source/_components/Nav.vue

• this component is duplicated here and in /request.... Consolidate.

src/pages/sign-in.vue

• when GH auth is complete, encapsulate duplicate UI from this and /sign-up

src/pages/data-source/_util.js

• update this util to use date-fns

src/pages/index.vue

• Uncomment the below to close pdap.io/issues/208; blocked by data-sources-app/issues/580

src/pages/data-request/[id].vue

• not found UI - do we want to send the user to search or something?

src/pages/search/_components/SearchResults.vue

• try to handle this with IntersectionObserver instead (i.e. set hash when div intersects, so hash remains up-to-date)
• decouple heading styling from heading level in design-system (or at least provide classes that can perform these overrides more efficiently)

src/pages/data-source/create.vue

• this component is massive. Let's break it up into components and move the constants and utils to separate files.
  ------ Also: the additional properties section is probably meaty enough that we want an async import.
  ------ Maybe even a separate sub-route? At .data-source/create/additional ?
  ------ Think about it.

src/pages/sign-up/index.vue

• when GH auth is complete, encapsulate duplicate UI from this and /sign-up

src/pages/data-source/[id].vue

• not found UI - do we want to send the user to search or something?

src/components/TypeaheadInput.vue

• Once this component is sufficiently generic, move to design-system?

src/components/tests/typeaheadinput.test.js

• set up test as above for complex items