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>`
Now the connection receive method preprends the last incomplete chunk
in the received buffer. This was made necessary by the new chunk
buffering in the SecureChannel.
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.
