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.

server/core/test/testlog.c

@@ -15,8 +15,8 @@
 #include <stdlib.h>
 #include <string.h>
 #include <maxscale/alloc.h>
-#include <skygw_utils.h>
-#include <log_manager.h>
+#include <maxscale/skygw_utils.h>
+#include <maxscale/log_manager.h>
 
 static void skygw_log_enable(int priority)
 {