[sdk/python] Transfer transaction - support for message types about symbol

[gimre-xymcity]

this is currently done via MessageEncoder object,
however, currently in case of NEM it will throw an error if it's instantiated on non-encrypted message type.
additionally try_decode/tryDecocde might throw in some cases

[cryptoBeliever]

Encrypting and decrypting message work correctly ✔️

encrypted = encoder.encode_deprecated(recipient_public_key, b'Some encrypted message')
print(encrypted.message)

# Create a transfer transaction
transfer = facade.transaction_factory.create({
	'type': 'transfer_transaction_v2',
	'signer_public_key': alicePubkey,
	'recipient_address': facade.network.public_key_to_address(bobKeyPair.public_key),
	'timestamp': networkTime.timestamp,
	'deadline': deadline,
	'fee': 200000,
	'amount': 1000000,
	'message': {
		'message_type': 'encrypted',
		'message': encrypted.message
	}
})

recipient_decoder = MessageEncoder(bobKeyPair)
decoded_message = recipient_decoder.try_decode(alicePubkey, encrypted)
print(decoded_message)

encrypted_message = message_encoder.encode(bobPubkey, b'message')
print(encrypted_message)

# Create a transfer transaction
transfer = facade.transaction_factory.create({
	'type': 'transfer_transaction_v1',
	'signer_public_key': alicePubkey,
	'recipient_address': facade.network.public_key_to_address(bobPubkey),
	'deadline': deadline,
	'fee': 100000,
	'mosaics': [],
	'message': b'\1' + bytes(encrypted_message[1::].hex(), 'utf-8') # workaround for old wallet (there is bug in old SDK that causes double encoding)
})