Add the flutter_sqlcipher plugin

[artob]

This is a Flutter plugin that bundles and wraps SQLCipher, an open-source extension to SQLite that provides transparent 256-bit AES encryption of database files.

• https://github.com/drydart/flutter_sqlcipher
• https://pub.dartlang.org/packages/flutter_sqlcipher
• https://pub.dartlang.org/documentation/flutter_sqlcipher/latest/

[Solido]

I've been thinking on this plugin, it's useful in some case but very specific on use cases and platform.
Thank you for PR !