Icons for VDM files in the explorer

[jonaskrask]

I think that this might only be possible through a dedicated "Icon theme" extension. However, it seems pretty easy to contribute to one of the largest icon themes in the marketplace: https://marketplace.visualstudio.com/items?itemName=vscode-icons-team.vscode-icons

Another option would be to just write a short configuration that users can put in their settings for the icon theme extension.

[FrederikPM]

This should also include icons for the dialects, however these icons can be provided directly by our extension.