Add a new M3 - Insecure Communication mobile app

## Motivation

SecDevLab's goal is to provide examples of how security vulnerabilities could be fixed, but we still don't have any examples of `Insecure Communication` from [OWASP's 2016 Mobile Top 10](https://owasp.org/www-project-mobile-top-10/).

## It would be great if

We had an app illustrating this vulnerability and how it could be exploited by an attacker.

## What we expect

The new app must have a complete `README.md` with all the steps on how to get the environment ready to run it, how it can be installed, and how an attacker could compromise it.

The app's `README.md` should be similar to the existing mobile apps, such as [this one](https://github.com/globocom/secDevLabs/blob/master/owasp-top10-2016-mobile/m5/panda_zap/README.md).

Note: The app doesn't need to be written in flutter/dart.

## Tips

* [M3 - Insecure Communication](https://owasp.org/www-project-mobile-top-10/2016-risks/m3-insecure-communication)
* [Design beautiful apps - Flutter](https://flutter.dev/)