Notify plugins when Cmdr or Beta status changes while the preferences dialog
is open.
Display a note on the Credentials tab when Cmdr is not set. Addresses #224
- New callback notify_prefs_changed
- Plugin can set settings tab name
- Plugin can return a pair of widgets for display in main window - typically (label, status)
Use nb or ttk widgets as appropriate for correct look-and-feel.
Print messages to stderr so they appear when the plugin is loaded by the
packaged Windows exe.
Do something with the example's main window widget.
