Streamline Setups UI

[mozjag]

Some ideas for streamlining Setups:

• If there's only one Setup, "Open Setup" could skip the picker.
• Updating a Setup could be streamlined by tracking the Setup loaded and starting the dialog out on "Update existing Setup" with it pre-selected. (If no Setup was loaded, still default to "Create new Setup", of course).
• Maybe move "Change Setups" from the Settings page to an Edit (Pencil?) button between "Open Setup" and the "Reveal config file ..." button.