Move headers from server/include to include/maxscale

- Headers now to be included as <maxscale/xyz.h>
- First step, no cleanup of headers has been made. Only moving
  from one place to another + necessary modifications.

avro/maxavro.c

@@ -15,7 +15,7 @@
 #include <string.h>
 #include <stdbool.h>
 #include "maxavro.h"
-#include <log_manager.h>
+#include <maxscale/log_manager.h>
 #include <errno.h>
 
 /** Maximum byte size of an integer value */