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/modules/routing/readwritesplit/rwsplit_tmp_table_multi.c

@@ -18,9 +18,9 @@
 #include <maxscale/alloc.h>
 
 /* Note that modutil contains much MySQL specific code */
-#include <modutil.h>
+#include <maxscale/modutil.h>
 
-#include <router.h>
+#include <maxscale/router.h>
 #include <readwritesplit.h>
 #include <rwsplit_internal.h>
 /**