Check if React instance was fully set up before emit event

[arthursz]

This pull request solves the following bugs:

• error that occurs because ReactContext#getJSModule was not protected by ReactContext#hasActiveCatalystInstance();
• error presented by React Native alert module which says "Tried to show an alert while not attached to an Activity" that was occurring when the application was in foreground and was opened by the notification;
• application was not sending notification events to React when in foreground and was opened by the notification in Android API < 21.