"Enter" and "installed" pings are wrongly generated after updating the browser

[motin]

This is a follow-up on the following issue:

• "Enter" and "installed" pings are wrongly generated after updating the browser florian/federated-learning-addon#6 - "Enter" and "installed" pings are wrongly generated after updating the browser - opened on 10 Jul 2018 by SoftVision-CarmenFat

First of all we need a documented decision on how "enter" and "installed" pings should be generated after updating the browser.

We should also investigate if updating the browser currently leads to general incorrect behavior such as study restarts or incorrect ending signals etc.

Depends on: #143