Transition to manifest v3

[ttyridal]

Google has proposed a new manifest with a couple of breaking changes to how masterpassword work

https://developer.chrome.com/docs/extensions/mv3/intro/mv3-overview/

Identified work that needs to be done

• [ ] Transition to service worker (background page will be depricated)

  • Needs the In-memory storage feature which is not yet done

• [ ] Verify that content scripts work as expected

Oh, and apparently there is a deadline: January'23