Aes wip

Updates in this pull request have:-
* Enabled CBC mode of encryption (Did try CTR, but had issues, but like idea of CBC over CTR).
* Use aes.c/aes.h files for functions
* Can now encrypt bunch of bytes of arbitrary length.
* Able to decrypt results as well.
* Demo of encryption/decryption in the main routine.
* Bit of a clean up.

Yes it works, but obviously more work required to incorporate this into the device properly.