.env to configure app

[levibostian]

To follow the twelve-factor app idea behind using a .env file to configure your app, setup project so that all you need to do is edit a .env file to configure it.

Tasks:

• [x] Install dotenv-android CLI to give access in the source code to .env values.
• [x] Create fastlane script that will take .env values for app name, package name, things like that and changes the Gradle config of the app to these values.
• [x] Create fastlane script that will generate app icons from .env value.

Resources:

• tool to make .env values exported on the system for tools like fastlane to access them.
• Fastlane app icon generator with adaptive icons help.

[levibostian]

Done. No adaptive icons, but that's ok for now.