subkey generation, feistel function and encrypting/decrypting of a blok with tests
Asynchronous encrypting/decrypting using CompetableFutures
Optimize S box function
Refactored encryption and decryption functions
Add decryption button and handler to GUI
Refactoring and optimization Feistel function
Merge remote-tracking branch 'origin/feature-des-decrypt'

Conflicts:
	src/main/java/cryptogen/CryptoGen.java
	src/main/java/cryptogen/DesEncryption.java
	src/main/java/cryptogen/Feistel.java
	src/main/java/cryptogen/KeyCalculator.java
	src/main/java/helpers/ByteHelper.java