Feature Request: Custom Icon

[newhinton]

Is your feature request related to a problem? Please describe.
Finding the correct Button

Describe the solution you'd like
I'd like to provide a custom image per button.
To do so, i'd like to have a button called "upload" that will allow me to select any image.
The image could be stored base64 as metadata.

Describe alternatives you've considered

Additional context

[newhinton]

To be precise:

I'd like the "thumbnail" in the switch list to have a custom icon, not the switch in the editor.
(If a thumbnail was set, it could be shown in the editor too, but only as a small icon somewhere)