Add HF propagation prediction

[martinhpedersen]

The primary goal of this feature is to provide a link quality indicator to the rmslist.

There are two models available: VOACAP and ITURHFProp. I'd like to support both at some time, but focusing on VOACAP for now because it's more familiar to hams and the installation process is more streamlined on both Windows, Linux and macOS. voacapl for Linux/mac and voacapw for Windows.