This commit drops the 'ua_' prefix and changes the public includes
to the form `#include <open62541/server.h>` instead of the old
`#include <ua_server.h>`
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.
Julius Pfrommer