expose navigation handleDeepLink as a static method (#727)

src/Navigation.js

 import PropRegistry from './PropRegistry';
 
 const registeredScreens = {};
+const _allNavigatorEventHandlers = {};
 
 function registerScreen(screenID, generator) {
   registeredScreens[screenID] = generator;
   return platformSpecific.startSingleScreenApp(params);
 }
 
+function setEventHandler(navigatorEventID, eventHandler) {
+  _allNavigatorEventHandlers[navigatorEventID] = eventHandler;
+}
+
+function clearEventHandler(navigatorEventID) {
+  delete _allNavigatorEventHandlers[navigatorEventID];
+}
+
+function handleDeepLink(params = {}) {
+  if (!params.link) return;
+  const event = {
+    type: 'DeepLink',
+    link: params.link
+  };
+  for (let i in _allNavigatorEventHandlers) {
+    _allNavigatorEventHandlers[i](event);
+  }
+}
+
 export default {
   getRegisteredScreen,
   registerComponent,
   showInAppNotification: showInAppNotification,
   dismissInAppNotification: dismissInAppNotification,
   startTabBasedApp: startTabBasedApp,
-  startSingleScreenApp: startSingleScreenApp
+  startSingleScreenApp: startSingleScreenApp,
+  setEventHandler: setEventHandler,
+  clearEventHandler: clearEventHandler,
+  handleDeepLink: handleDeepLink
 };

src/Screen.js

 import platformSpecific from './deprecated/platformSpecificDeprecated';
 import Navigation from './Navigation';
 
-const _allNavigatorEventHandlers = {};
-
 const NavigationSpecific = {
   push: platformSpecific.navigatorPush,
   pop: platformSpecific.navigatorPop,
     if (!this.navigatorEventSubscription) {
       let Emitter = Platform.OS === 'android' ? DeviceEventEmitter : NativeAppEventEmitter;
       this.navigatorEventSubscription = Emitter.addListener(this.navigatorEventID, (event) => this.onNavigatorEvent(event));
-      _allNavigatorEventHandlers[this.navigatorEventID] = (event) => this.onNavigatorEvent(event);
+      Navigation.setEventHandler(this.navigatorEventID, (event) => this.onNavigatorEvent(event));
     }
   }
 
   handleDeepLink(params = {}) {
-    if (!params.link) return;
-    const event = {
-      type: 'DeepLink',
-      link: params.link
-    };
-    for (let i in _allNavigatorEventHandlers) {
-      _allNavigatorEventHandlers[i](event);
-    }
+    Navigation.handleDeepLink(params);
   }
 
   onNavigatorEvent(event) {
   cleanup() {
     if (this.navigatorEventSubscription) {
       this.navigatorEventSubscription.remove();
-      delete _allNavigatorEventHandlers[this.navigatorEventID];
+      Navigation.clearEventHandler(this.navigatorEventID);
     }
   }
 }