Added Zend\Crypt\FileCipher for file encryption/decryption

According to this [refactor](https://github.com/zendframework/zf2/pull/6410#issuecomment-47108687), I added a new class `Zend\Crypt\FileCipher` for the encryption/decryption of files.
Moreover in this [commit](https://github.com/ezimuel/zf2/commit/3f49a6b3afd95e73d140f4d9380ee11a93ad8995),  I removed the compression part to prevent potential information leakage (e.g. [CRIME](http://en.wikipedia.org/wiki/CRIME) attack).

The main methods of this class can be used to encrypt/decrypt a file:
- `encrypt($fileIn, $fileOut)`
- `decrypt($fileIn, $fileOut)`

where `$fileIn` is the input file to encrypt/decrypt and `$fileOut` is the output file. 
The  `Zend\Crypt\FileCipher` component can be used to encrypt/decrypt files of any dimension. I used a buffer memory of 1 MB to read the files, block by block.The encryption of file follows the same procedure of `Zend\Crypt\BlockCipher::encrypt`, using **encryption-then-authenticate** approach with HMAC (SHA256 by default).
I'd actually keep away from that, to be honest. Since this is all new API, I'd actually add the feature only if requested later on.
Allowing a string here seems overkill and unneeded complexity