expose clearing all buttons to lua

src/ui/script_ui.cpp

@@ -861,6 +861,18 @@ void CallHandler(unsigned int handle, int value)
 	lua_pop(Lua, 1);
 }
 
+/**
+**  Clear all buttons
+**
+**  @param l  Lua state.
+*/
+static int CclClearButtons(lua_State *l)
+{
+	LuaCheckArgs(l, 0);
+	CleanButtons();
+	return 0;
+}
+
 /**
 **  Define a button.
 **
@@ -1192,6 +1204,7 @@ void UserInterfaceCclRegister()
 	lua_register(Lua, "SetFancyBuildings", CclSetFancyBuildings);
 
 	lua_register(Lua, "DefineButton", CclDefineButton);
+	lua_register(Lua, "ClearButtons", CclClearButtons);
 
 	lua_register(Lua, "DefineButtonStyle", CclDefineButtonStyle);