Export interfaces

This commit exports interfaces used by RNN so they can be used to improve type checking. closes #4177

Usage

import {Options} from 'react-native-navigation';
const options: Options = {}

lib/src/index.ts

@@ -3,3 +3,9 @@ import { Navigation as NavigationClass } from './Navigation';
 const singleton = new NavigationClass();
 
 export const Navigation = singleton;
+export * from './adapters/Constants';
+export * from './interfaces/ComponentEvents';
+export * from './interfaces/Events';
+export * from './interfaces/EventSubscription';
+export * from './interfaces/Layout';
+export * from './interfaces/Options';