Convert Session Expired Warning/Error Dialog to mixed in of CoMPAS OpenSCD

[dlabordus]

Describe the bug
When a session is about to expire or is expired two dialogs are displayed. These are now added by a change in the OpenSCD Element, it would be nice to create a mixed-in for this and add this mixed-in to the OpenSCD Element.
If the new OpenSCD Core is avaliable and CoMPAS OpenSCD isn't a fork anymore this will making a switch to the new core easier.
Also included functionality to load the User Information and NSDoc Files in this mixed-in. These two are now sneaky loaded when the CoMPAS Settings Plugin is loaded.

Expected behavior
Create a CoMPAS mixed-in to add the dialogs to the application and add this mixed-in to the OpenSCD Element.
Remove the logic to add the dialogs from the OpenSCD Render function.
Also put logic for loading the User Info and NSDoc Files from the CoMPAS Backend service to this mixed-in.