First pass at multiple projects with temporary UI

[microbit-robert]

This is a first pass at storing multiple projects and builds on the storage branch which transitions from using localStorage to IndexedDB. There may well be bugs in this implementation, please document these if you hit them during testing.

If additional code changes are made, you will probably need to manually delete the "ml" database in IndexedDB using devtools.

TODO:

• Testing, lots of testing
• UI design / changes
  • Consider project cards (date and id are for debugging purposes at the moment / image / icons), capturing project name upfront, importing data with a choice to create a new project or append or replace actions in existing project
• Look at the diff with the storage branch to determine what changes need to be pulled in for an easy migration from single to multiple projects
• Work out why e2e test was failing (commented out for now - it relates to the resume session button which is probably going away, but nice to understand why it was failing
• Add e2e tests
• More consideration and testing of cross-tab changes
• Investigate localStorage migration bug
  • To reproduce the bug, clear ml database in IndexedDB, add project to localStorage under 'ml' name, then refresh the page.
• ...

[github-actions]

Preview build will be at
https://review-createai.microbit.org/storage-multiple/