certificate: Return signature scheme and parameters from issued_by() method

This also required some include restructuring (avoid including library.h
in headers) to avoid unresolvable circular dependencies.

src/charon-tkm/src/tkm/tkm_private_key.c

@@ -14,6 +14,7 @@
  * for more details.
  */
 
+#include <library.h>
 #include <utils/debug.h>
 #include <tkm/constants.h>
 #include <tkm/client.h>

src/charon-tkm/src/tkm/tkm_public_key.c

@@ -14,6 +14,7 @@
  * for more details.
  */
 
+#include <library.h>
 #include <utils/debug.h>
 
 #include "tkm_public_key.h"