Warning instead of Error in case of no NSDoc files are found; More descriptive warning message

[pascalwilbrink]

When no NSDoc files are found, a log Event and a snackbar are shown in the frontend.

The snackbar should be removed.
We should check with openscd if we want to divide logging an Error and showing the Snackbar in the bottom into 2 seperate things or that we want to add a flag to the event to skip showing the snackbar

[Sander3003]

If I open demo.compas.energy right now, this is what I see:

The console states:

As an CoMPAS user
I would like to see more clear warning messages
In order to judge if the tool is stable enough to build substations

Posposed solution:
Process NSD loading erros as warning
Add more detail to the waning: Cannot load file XYZ