Added compatibility to the manager with Ubuntu 20.04 & 18.04

To use it:

Super flexible, should work with all Ubuntu 14.04-20.04. (I only tested 14/16/18/20 LTS

no special dependencies for Ubuntu 16-20, but you might need to install gtk+3 for Ubuntu 14.04, its available in the repos though. (libgtk-3-0)

built with gtk+3 so No Lag in any OS, even 20.04, and better future proofed