Activity storage should be recreated from scratch if user changes auth token

[iarovikov]

Currently if user changes auth token on activity, it then goes through followup configuration but in this case activity storage should be cleared and initial configuration should take place.
A simple way to see the wrongdoings of current approach is like this: add Slack activity to plan, authorize it with our old Slack team. Select some channel or user in activity UI. No reauthorize activity to use our current Slack team. You will still see the list of channels and users from the first authorization