Show dialog when user did not log out

Description / Overview

When a user logs out there are some crucial things that need to be taken care of such as freeing reserved subscriptions. However, if a user closes the window or kills the browser without logging out, these tasks are not performed which will bring up some issues. This dialog will help preventing the user from closing the browser without logging out.

Links / references

The vue instance accepts a created hook where eventhandlers can be addded
https://developer.mozilla.org/en-US/docs/Web/API/Window/beforeunload_event