switch to one-way-binding in form

ui/hv2-ui/src/app/account/account.component.html

@@ -1,24 +1,24 @@
 <div id="firstBlock">
-<form (ngSubmit)="addAccountEntry()">
+<form (ngSubmit)="addAccountEntry(userForm)" #userForm="ngForm">
 <mat-form-field appearance="outline" id="addEntryfield">
     <mat-label>Datum</mat-label>
-    <input matInput name="createdAt" [(ngModel)]="newAccountEntry.created_at" [matDatepicker]="createdAtPicker"/>
+    <input matInput ngModel name="createdAt" [matDatepicker]="createdAtPicker"/>
     <mat-datepicker-toggle matSuffix [for]="createdAtPicker"></mat-datepicker-toggle>
     <mat-datepicker #createdAtPicker></mat-datepicker>
 </mat-form-field>
 <mat-form-field appearance="outline">
     <mat-label>Kategorie</mat-label>
-    <mat-select [(ngModel)]="newAccountEntry.account_entry_category" name="category" [disabled]="shallBeRentPayment">
+    <mat-select ngModel name="category" [disabled]="shallBeRentPayment">
         <mat-option *ngFor="let p of accountEntryCategories" [value]="p.id">{{p.description}}</mat-option>
     </mat-select>
 </mat-form-field>
 <mat-form-field appearance="outline">
     <mat-label>Betrag (€)</mat-label>
-    <input matInput type="number" name="amount" [(ngModel)]="newAccountEntry.amount"/>
+    <input matInput type="number" name="amount" ngModel/>
 </mat-form-field>
 <mat-form-field appearance="outline">
     <mat-label>Beschreibung</mat-label>
-    <input matInput name="description" [(ngModel)]="newAccountEntry.description"/>
+    <input matInput name="description" ngModel/>
 </mat-form-field>
 <button #addAccountEntryButton type="submit" mat-raised-button color="primary">Buchung speichern</button>
 </form>