Support showing checkboxes or radio buttons in menus

For checkboxes it probably doesn't really make sense to use them yet, because
we'd have to find a way how you can toggle them without closing the dialog; but
we already provide rendering for them to lay the ground.

But radio buttons can be used already, because for those it is ok to close the
dialog when choosing a different option (as long as there is only one grounp of
radio buttons in the panel, that is).

pkg/gui/types/common.go

@@ -217,6 +217,30 @@ type DisabledReason struct {
 	ShowErrorInPanel bool
 }
 
+type MenuWidget int
+
+const (
+	MenuWidgetNone MenuWidget = iota
+	MenuWidgetRadioButtonSelected
+	MenuWidgetRadioButtonUnselected
+	MenuWidgetCheckboxSelected
+	MenuWidgetCheckboxUnselected
+)
+
+func MakeMenuRadioButton(value bool) MenuWidget {
+	if value {
+		return MenuWidgetRadioButtonSelected
+	}
+	return MenuWidgetRadioButtonUnselected
+}
+
+func MakeMenuCheckBox(value bool) MenuWidget {
+	if value {
+		return MenuWidgetCheckboxSelected
+	}
+	return MenuWidgetCheckboxUnselected
+}
+
 type MenuItem struct {
 	Label string
 
@@ -232,6 +256,12 @@ type MenuItem struct {
 	// item, as opposed to having to navigate to it
 	Key Key
 
+	// A widget to show in front of the menu item. Supported widget types are
+	// checkboxes and radio buttons,
+	// This only handles the rendering of the widget; the behavior needs to be
+	// provided by the client.
+	Widget MenuWidget
+
 	// The tooltip will be displayed upon highlighting the menu item
 	Tooltip string