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.

include/maxscale/limits.h

@@ -0,0 +1,24 @@
+#ifndef _MAXSCALE_LIMITS_H
+#define _MAXSCALE_LIMITS_H
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+// This file defines hard limits of MaxScale.
+
+// Thread information is stored in a bitmask whose size must be a
+// multiple of 8. The bitmask is indexed using the thread id that start
+// from 1. Hence, the hard maximum number of threads must be a
+// multiple of 8 minus 1.
+#define MXS_MAX_THREADS 255
+
+#endif