Lib: Improve VirgilSymmetricCipher class description.
Lib: Add method to the class VirgilByteArray that allows zeroize it.
Lib: Add finalization method to the VirgilChunkCipher class.
Lib: Add method to the class VirgilCipher that allows re-encrypt (change owner) the encription key.
PHP: Add unit test to cover VirgilCipher::rencryptKey method.
AS3: Add wrappers for methods: VirgilCipher::reencryptKey and VirgilChunkCipher::finalize.