Add countdown before logout due to inactivity

[refi93]

Currently the wallet logs off abruptly after 15 minutes of inactivity which can lead to weird glitches if the user happens to perform an action right at that moment. The logout is also quite abrupt, so it may make sense to show a countdown before the log-out happens. We should also check out the timing and make sure to show the log-out notification before actually clearing the state of the wallet.

We actually had a report of a Cannot read property 'getAccountsInfo' of null from a user which apparently related to the logout after 15 minutes