Migrate lookup term out of app state

[didoesdigital]

This PR moves lookupTerm out of app state to continue the work of breaking up app.js.

Changes:

• In app.js, if the location pathname includes /lookup, we no longer clear the query params
• When visiting a bookmarked lookup URL like https://didoesdigital.com/typey-type/lookup?q=had%20the, Typey Type no longer clears the query param after arriving
• When entering words to look up, the query param is updated (with debouncing).

Given the last point above, it's no longer necessary to manually provide a share link because you can now copy and paste the URL from the browser without it:

Let's keep the manual copy button for now anyway, to encourage people to share Typey Type lookup links.

The PR also changes:

• lookup stories
• extracts the debounce function to its own file