[CSM] Client side modding

* rename GameScripting to ServerScripting
* Make getBuiltinLuaPath static serverside
* Add on_shutdown callback
* Add on_receiving_chat_message & on_sending_chat_message callbacks
* ScriptApiBase: use IGameDef instead of Server
  This permits to share common attribute between client & server
* Enable mod security in client side modding without conditions

src/script/lua_api/l_client.h

@@ -0,0 +1,36 @@
+/*
+Minetest
+Copyright (C) 2013 celeron55, Perttu Ahola <celeron55@gmail.com>
+Copyright (C) 2017 nerzhul, Loic Blot <loic.blot@unix-experience.fr>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#ifndef L_CLIENT_H_
+#define L_CLIENT_H_
+
+#include "lua_api/l_base.h"
+
+class ModApiClient : public ModApiBase
+{
+private:
+	// get_current_modname()
+	static int l_get_current_modname(lua_State *L);
+
+public:
+	static void Initialize(lua_State *L, int top);
+};
+
+#endif