Disable layer switcher actions on non-base layers

Closes #216

src/components/popover/popover.component.ts

@@ -67,6 +67,7 @@ enum TabName {
 export class PopoverComponent implements OnChanges {
     @Input() defaultKeyAction: KeyAction;
     @Input() currentKeymap: Keymap;
+    @Input() currentLayer: number;
     @Input() keyPosition: ClientRect;
     @Input() wrapPosition: ClientRect;
     @Input() visible: boolean;