Add a Show Contacts button to the AlphaFold PAE error plot

[Tom Goddard]

It would be nice to have a "Show Contacts" button on the AlphaFold PAE error plot panel that runs the command "alphafold contacts #<model_id>" which will show pseudobonds for all close pairs of residue colored by PAE. Probably the button should change to "Hide Contacts" after they are shown.

This is a pretty useful way to visualize PAE directly on the structure to see if interfaces between molecules are confidently predicted.

It might be nice to issue the command with the "distance 3 radius 0.5" options so the user can see how to change those parameters by looking at the log.