add subnet mask IP support for maintenance mode

Author: Anton Evers

composer.json

@@ -75,7 +75,8 @@
         "zendframework/zend-text": "^2.6.0",
         "zendframework/zend-uri": "^2.5.1",
         "zendframework/zend-validator": "^2.6.0",
-        "zendframework/zend-view": "^2.8.1"
+        "zendframework/zend-view": "^2.8.1",
+        "darsyn/ip": "^3.3"
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "~2.1.1",