v2.1: refactor(app): maintain `projects` state variable

- Promote `projects` state variable from `Projects.js` (the prior
  landing page) to `App.js`.
- Pass `projects` as props to two pages of site, `Home.js` and
  `Portfolio.js`.
- Render only highlighted (pinned/starred) projects on `Home.js`.
- Render all active projects on `Portfolio.js`