Added the file encryption/decryption to Zend\Crypt

This PR replace the https://github.com/zendframework/zf2/pull/6410 with a new `FileCipher` implementation based on the suggestion of #6410. I removed the fluent interface and other methods not really relevant for the usage of this component. I also improved the unit tests adding the one for `Zend\Crypt\Symmetric\Padding\NoPadding`.
I also provided the documentation for this new component in this PR https://github.com/zendframework/zf2-documentation/pull/1311
This property always exists (setted in constructor), can be only null but that's ok.