[winswitch] Install python3-only xpra

[Σταύρος Ντέντος]

Hello there,

On a new Ubuntu 18.04 system, I do:

$ sudo apt-get install xpra python3-xpra

However, among numerous packages, I am getting:

[...] python2-xpra [...]

Why is that? Isn't / Should there be an easier way to install python3-only
xpra?

I understand your need to support it, but AFAIK you are also saying that
Py3 is fully supported and working.

Ντέντος Σταύρος