2.4.0

Upgrade FlySystem 2.0 (#21)

* Align with atk 2.4

* Add php-cs-fixer

* Align to 2.4 and cleanup

* Add helper class for View and Download of files

* typo old namespace

* Update readme with new namespace

* Renamed basic.php to index.php

* Add headers normalize

* Typo classname

* Upgrade FlySystem 2.0