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/memlog.c

@@ -22,13 +22,13 @@
  *
  * @endverbatim
  */
-#include <memlog.h>
+#include <maxscale/memlog.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdint.h>
 #include <maxscale/alloc.h>
-#include <log_manager.h>
+#include <maxscale/log_manager.h>
 
 static MEMLOG *memlogs = NULL;
 static SPINLOCK memlock = SPINLOCK_INIT;