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
@staabm The Pbkdf2 algorithm used in the encryption/decryption operations of FileCipher is used only to generate the encryption and authentication keys. That means only one time for each execution. I used a value of 10'000 as default and it's actually very low (about 0.05 sec, using an Intel i5 at 3.30GHz, you can check by yourself using [this code](https://gist.github.com/ezimuel/0769f99e45a04e124cf0)). The blog post that you referred has clearly wrong numbers.