Parse lastStamp as Date in AvailabilityService

Type AvailabilityInfo.lastStamp as Date and convert from the JSON
string in the service after fetch, so consumers work with real
Date objects.

client/src/availability-info.ts

@@ -2,6 +2,6 @@ export class AvailabilityInfo {
   public user: string;
   public loggedIn: boolean;
   public extension: string;
-  public lastStamp: string;
+  public lastStamp: Date;
   public firma: boolean;
 }

client/src/availability-service.ts

@@ -33,7 +33,11 @@ export class AvailabilityService {
     try {
       var response = await GM_fetch(Config.tapi_server_url + '/availability')
       if (response.status === 200) {
-        this._availabilities = await response.json() as AvailabilityInfo[]
+        var raw = await response.json() as AvailabilityInfo[]
+        this._availabilities = raw.map(a => ({
+          ...a,
+          lastStamp: a.lastStamp ? new Date(a.lastStamp) : null,
+        }))
         this._listeners.forEach(l => l(this._availabilities))
       }
     } catch (error) {

client/src/availability.ts

@@ -67,8 +67,8 @@ export class Availability {
     var dotClass = entry.loggedIn ? 'tapi-dot-on' : 'tapi-dot-off'
     var time = ''
     if (entry.lastStamp) {
-      var d = new Date(entry.lastStamp)
       var pad = (n: number) => n.toString().padStart(2, '0')
+      var d = entry.lastStamp
       time = pad(d.getDate()) + '.' + pad(d.getMonth() + 1) + '. ' + pad(d.getHours()) + ':' + pad(d.getMinutes())
     }
     var location = ''