Block Cipher python implementation

[pyGuru123]

1> Implement a Block Cipher encryption and decryption method and wrap it inside a class BlockCipher
2> save it to block_cipher.py
3> put the file inside decrypto/src folder
4> submit a PR.

Sample implementation : https://github.com/pyGuru123/Decrypto/blob/main/decrypto/src/binary_cipher.py
strictly follow above implementation and PEP8 Guidelines