Revisit `onActive` and `onInactive`

We should revisit the `onActive` and `onInactive` handlers at some point to come up with a better signal for the client being inactive.

Currently it is flagged as inactive as soon as the extension window is closed, but users may close it to view a dapp, opening it seconds/minutes later.

We may also choose to implement new handlers for this case. 

Blocked for now.