Improve usability

[dbosk]

Add a lab where they're asked to develop some simple application. They must use cryptography, primitives from the first few lectures.

Then they should evaluate how secure they think that their implementation is.

Then they get to read "Comparing the Usability of Cryptographic APIs".

Then we can have the seminar on usability.

We can repurpose the AES implementation lab to add a focus on usable library.