Creates the configure widget for the plugin. The returned widget
should allow configuring all the relevant aspects of the plugin, and should
allow instant-apply, as promoted by the Gnome Human Interface Guidelines.
#PeasGtkPluginManager will embed the returned widget into a dialog box,
but you shouldn't take this behaviour for granted as other implementations
of a plugin manager UI might do otherwise.
This method should always return a valid #GtkWidget instance, never %NULL.
Creates the configure widget for the plugin. The returned widget should allow configuring all the relevant aspects of the plugin, and should allow instant-apply, as promoted by the Gnome Human Interface Guidelines.
#PeasGtkPluginManager will embed the returned widget into a dialog box, but you shouldn't take this behaviour for granted as other implementations of a plugin manager UI might do otherwise.
This method should always return a valid #GtkWidget instance, never %NULL.
Return: A #GtkWidget used for configuration.