Define externally accessible contants with 'var' instead of 'const'

Just as we did with classes, define other constants that are (or
may be) used from other modules with 'var' to cut down on warnings.

https://bugzilla.gnome.org/show_bug.cgi?id=785084

js/ui/status/network.js

@@ -40,14 +40,14 @@ const NMAccessPointSecurity = {
     WPA2_ENT: 6
 };
 
-const MAX_DEVICE_ITEMS = 4;
+var MAX_DEVICE_ITEMS = 4;
 
 // small optimization, to avoid using [] all the time
 const NM80211Mode = NetworkManager['80211Mode'];
 const NM80211ApFlags = NetworkManager['80211ApFlags'];
 const NM80211ApSecurityFlags = NetworkManager['80211ApSecurityFlags'];
 
-const PortalHelperResult = {
+var PortalHelperResult = {
     CANCELLED: 0,
     COMPLETED: 1,
     RECHECK: 2