Class 21. Using Firebase with Flutter

<li>Installation
<li>Using Firestore as backend:<br/>
&nbsp;&nbsp;&nbsp;+ Building the backend, frontend<br/>
&nbsp;&nbsp;&nbsp;+ Working with data<br/>
&nbsp;&nbsp;&nbsp;+ Transactions and batches<br/>
<li>Monetizing your apps with AdMob<br/>
&nbsp;&nbsp;&nbsp;+ Ad banners<br/>
&nbsp;&nbsp;&nbsp;+ Rewarded video ads<br/>
<li>Flutter & Google ML Kit<br/>
&nbsp;&nbsp;&nbsp;+ Face Detection, Object Detection and Tracking, Pose Detection<br/>
&nbsp;&nbsp;&nbsp;+ Image Labeling<br/>
&nbsp;&nbsp;&nbsp;+ Bar-code scanning<br/>
&nbsp;&nbsp;&nbsp;+ Text Regconition<br/>
<li>Push Notifications with FCM: handling and sending push notifications
<li>Authenticating with Firebase