Improve filterBar on eventsPage, improve API access from frontend

software/src/data/models/acts/eventModel.ts

@@ -6,6 +6,6 @@ export class EventModel {
   name: string
   offered: boolean
   image: string
-  band: BandModel
-  concerts: Array<ConcertModel>
+  band: BandModel = new BandModel()
+  concerts: Array<ConcertModel> = [ new ConcertModel() ]
 }

software/src/data/models/locations/cityModel.ts

@@ -2,15 +2,21 @@
  * Replica of the API endpoint /cities
  */
 export class CityModel {
-  id: number
-  name: string
-  country: string
-  image: string
+  id: number = -1
+  name: string = ""
+  country: string = ""
+  image: string = ""
   locations: Array<{
     id: number
     name: string
     address: string
     image: string
     nrOfConcerts: number
-  }>
+  }> = [{
+    id: -1,
+    name: "",
+    address: "",
+    image: "",
+    nrOfConcerts: 0
+  }]
 }