Update activity_encryption/.gitkeep, activity_encryption/00_trainer-guide.md, activity_encryption/printable_caesar-cipher-wheel.pdf, activity_encryption/printable_enigma-tube.pdf, activity_encryption/printable_vigenere-cypher-otp.pdf

Update Activity: Encryption/printable_caesar-cipher-wheel.pdf, Activity: Encryption/printable_vigenere-cypher-otp.pdf