ui: Use localStorage instead of sessionStorage for refresh interval + collapsed groups

Fixes #509

Supersedes #510

web/app/src/components/EndpointGroup.vue

@@ -60,7 +60,7 @@ export default {
     },
     toggleGroup() {
       this.collapsed = !this.collapsed;
-      sessionStorage.setItem(`gatus:endpoint-group:${this.name}:collapsed`, this.collapsed);
+      localStorage.setItem(`gatus:endpoint-group:${this.name}:collapsed`, this.collapsed);
     },
     showTooltip(result, event) {
       this.$emit('showTooltip', result, event);
@@ -80,7 +80,7 @@ export default {
   data() {
     return {
       unhealthyCount: 0,
-      collapsed: sessionStorage.getItem(`gatus:endpoint-group:${this.name}:collapsed`) === "true"
+      collapsed: localStorage.getItem(`gatus:endpoint-group:${this.name}:collapsed`) === "true"
     }
   }
 }

web/app/src/components/Settings.vue

@@ -33,7 +33,7 @@ export default {
   props: {},
   methods: {
     setRefreshInterval(seconds) {
-      sessionStorage.setItem('gatus:refresh-interval', seconds);
+      localStorage.setItem('gatus:refresh-interval', seconds);
       let that = this;
       this.refreshIntervalHandler = setInterval(function () {
         that.refreshData();
@@ -78,7 +78,7 @@ export default {
   },
   data() {
     return {
-      refreshInterval: sessionStorage.getItem('gatus:refresh-interval') < 10 ? 300 : parseInt(sessionStorage.getItem('gatus:refresh-interval')),
+      refreshInterval: localStorage.getItem('gatus:refresh-interval') < 10 ? 300 : parseInt(localStorage.getItem('gatus:refresh-interval')),
       refreshIntervalHandler: 0,
       darkMode: true
     }