Throttle snack notifications

lib/www/client/source/src/components/footer.vue

@@ -60,6 +60,13 @@ export default {
     DougalNotificationsControl
   },
 
+  data () {
+    return {
+      lastGatewayErrorTimestamp: 0,
+      gatewayErrorSilencePeriod: 60000,
+    }
+  },
+
   computed: {
     year () {
       const date = new Date();
@@ -77,7 +84,11 @@ export default {
 
     isGatewayReliable (val) {
       if (val === false) {
-        this.$root.showSnack("Gateway error", "warning");
+        const elapsed = Date.now() - this.lastGatewayErrorTimestamp;
+        const lastGatewayErrorTimestamp = Date.now();
+        if (elapsed > this.gatewayErrorSilencePeriod) {
+          this.$root.showSnack("Gateway error", "warning");
+        }
       }
     }