Add license expiry messages (#3153)

webapp/utils/constants.jsx

@@ -750,5 +750,7 @@ export default {
     MHPNS: 'https://push.mattermost.com',
     MTPNS: 'http://push-test.mattermost.com',
     BOT_NAME: 'BOT',
-    POST_COLLAPSE_TIMEOUT: 1000 * 60 * 5 // five minutes
+    POST_COLLAPSE_TIMEOUT: 1000 * 60 * 5, // five minutes
+    LICENSE_EXPIRY_NOTIFICATION: 1000 * 60 * 60 * 24 * 15, // 15 days
+    LICENSE_GRACE_PERIOD: 1000 * 60 * 60 * 24 * 15 // 15 days
 };