support for encrypted ints + ipaddresses / use null crypto authentic…

[dirkm]

• change the code generator to support encrypted int-types and ip-addresses. This implements the enhancement https://github.com/layeh/radius/issues/74
• differentiate between client and server authenticators to encrypt/decrypt packages. The CryptoAuthenticator can be nil if there are no encrypted packages
• added some test-cases in a new package cryptotest
• use null-authenticators when required (example CoARequest)

This code has been tested internally. Feel free to merge or offer some suggestions for improvements

[dweidenfeld]

@bontibon do you see any chance to get this merged? As far as I can see all open comments are resolved by now.