Need to integrate Notification with firebase for Meetings and chats

[Mehul175]

Need to send notifications to the user of meeting requests and accpt and declined

1. Need to setup firebase and send notification to mobile devices
2. Store Devicetoken and and udid of device for uniqueidentification of devices

refrence
https://github.com/wpeventmanager/wpem-organizer-app/issues/571

[ritakikani]

wpeventmanager@gmail.com
WpEvent2@2@