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).
Well, the point is that all these getters are usually only needed in rare contexts (and it can be avoided even there). Here, we're introducing new public API that we can't remove/change later on because of BC breaks.