Delayed display of configured slots when working with infinite scrolling

[spossner]

Description

When working with a larger amount of slots which are not in the dom from the very beginning, the current (non dynamic configuration) approach defines and displays all configured slots when setting up gpt. Due to GPTs API reference, slots must be in the dom before calling display. This is violated in the scenario above and ends in console warning messages.

Solution / Proposal

I have introduced a delayed display "list" which stores all IDs of AdvertisingSlots which are defined (in setupGpt) but not yet found in the dom.
When it comes to activation, such slots are displayed before doing the GPT refresh.
Therefore I have refactored the machinsm into a separate displayAndRefreshSlots function

(I have also upgraded the node version to LTS in order to avoid an outdated ssl issue in webpack plus bumped some package versions to avoid vulnerabilities)

[spossner]

Just realized that the tests are not executed while building - and they break because the display method of GPT is not called anymore if div is not available in dom (as it probably is the case for the jest tests). Need to review that first. -> moved PR back in draft