Implement AES encryption of the data block.

Implement AES encryption of the data block.

First try. This runs on 16 bytes long AES block size, and enlarges the
data block with 16 bytes, to make sure all bytes are in. The added
bytes are filled with '.'. It then creates a header featuring the new
length to be send, and finally sends the data block, then returns.

This code is untested, as creating the receiver will be my next step.

To simplify traffic_analyzer's code, this code should run as a function.
It's on the do-to-list.