feat(background-geolocation): add showAppSettings function

closes #548

src/plugins/background-geolocation.ts

@@ -287,11 +287,17 @@ export class BackgroundGeolocation {
   @Cordova()
   static isLocationEnabled(): Promise<number> { return; }
 
+  /**
+   * Display app settings to change permissions
+   */
+  @Cordova({ sync: true })
+  static showAppSettings(): void { }
+
   /**
    * Display device location settings
    */
-  @Cordova()
-  static showLocationSettings() { }
+  @Cordova({ sync: true })
+  static showLocationSettings(): void  { }
 
   /**
    * Method can be used to detect user changes in location services settings.