Create/Delete Virtual Displays

### Problem

I'd love to use another device such as a tablet as external monitor together with my laptop for work while on the go. To do so, I came across [Deskscreen](https://deskreen.com/lang-en) which allows one to do that - but for the second device to be used as desktop extension rather than just mirroring, we need to configure a virtual display which can be mirrored to the external device.

### Proposal

It would be great to be able to add/edit/remove virtual displays from within the existing switchboard plug. This might be beneficial for other use cases such as TeamViewer sessions or similar.

I'm aware that "Managing Virtual Displays" might sound too techy for the average user, so if we going to implement this in the plug we also want to make sure the user knows what this is for (maybe with some example use cases explained before the first virtual display is added).

### Prior Art (Optional)

There is a bash script created by @dianariyanto which adds some basic support for virtual display management:

https://github.com/dianariyanto/virtual-display-linux