* Always use functions to get sizes and lengths.
This makes for better encapsulation and unifies the interface usage for
asymmetric and symmetric modules
* Add nonce length to SecurityPolicy and use it.
Previousely the key length was used as nonce length, which was
incorrect.
This only worked for basic128rsa15.
* Add certificate signing algorithm to interface
* Remove unnecessary functions from SecurityPolicy interface
* allow session to switch over to a new securechannel
New tests that test for correct message structure and correct padding calculation.
Also, it is now possible to set key sizes and so forth in each test.
Defaults are provided by the setup functions.
The testing NetworkLayer now writes the data it 'Sends' into a buffer,
so we can check the buffer in our unit tests.
The new test checks if the headers etc. are encoded correctly and
if the encryption functions are called for the correct data.
* simplify client securechannel test
* rename sleeping on simulated testing clock to UA_fakeSleep
* let the server start before calling with the client
Stefan Profanter