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>`
Make use of EXIT_SUCCESS and EXIT_FAILURE from stdlib.h.
The previous approach of returning a value from UA_StatusCode
was often broken as an exit code can (portably) only be between 0 and 125.