form field validation (much better error messages)

src-ui/src/app/components/common/input/text/text.component.html

@@ -1,5 +1,8 @@
 <div class="form-group">
   <label [for]="inputId">{{title}}</label>
-  <input type="text" class="form-control" [id]="inputId" [(ngModel)]="value" (change)="onChange(value)">
+  <input type="text" class="form-control" [class.is-invalid]="error" [id]="inputId" [(ngModel)]="value" (change)="onChange(value)">
   <small *ngIf="hint" class="form-text text-muted">{{hint}}</small>
+  <div class="invalid-feedback">
+    {{error}}
+  </div>
 </div>