input: Write a function to create an application in Python for encryption and decryption of strings. The application should take a string as input and use the AES algorithm in ECB mode for encryption and decryption. The function should return two functions, one for encryption and one for decryption.
  assert encrypt('Hello World')
  assert decrypt(encrypt('Hello World'))=='Hello World'
  assert encrypt('')
  assert decrypt(encrypt(''))==''
output: def create_aes_ecb_app(key):
      from Crypto.Cipher import AES
      from Crypto.Util.Padding import pad, unpad
  
      def encrypt(plaintext):
          cipher = AES.new(key.encode(), AES.MODE_ECB)
          padded_plaintext = pad(plaintext.encode(), AES.block_size)
          ciphertext = cipher.encrypt(padded_plaintext)
          return ciphertext
  
      def decrypt(ciphertext):
          cipher = AES.new(key.encode(), AES.MODE_ECB)
          padded_plaintext = cipher.decrypt(ciphertext)
          plaintext = unpad(padded_plaintext, AES.block_size)
          return plaintext.decode()
  
      return encrypt, decrypt