With the new API changes in pd-buddy-python 0.5.0, a few fixes were
necessary to make the GUI work without errors again.  Among these were
creating a SinkConfig object with the new attributes, and adding list
rows for PPS APDOs.  Coming up next: voltage range support!

The last commit requires >=0.4.2, but I forgot to update the README to
say that.

Assuming the power supply follows the Power Rules, it's a lot more
informative to show its PDP than the number of PDOs it advertises.  This
is the first step towards implementing the new design for showing the
Source_Capabilities.

The GUI still works fine with version 0.1, but should be used with 0.2
now that the PID is assigned.

The program structure is no better yet, but it uses the slick new
library I made.