added dropdown component and service. not functional yet

src/app/services/XAService.service.ts

@@ -0,0 +1,17 @@
+import { BehaviorSubject } from 'rxjs';
+import { Injectable } from '@angular/core';
+
+@Injectable({
+    providedIn: 'root'
+})
+export class XAService {
+
+    // private selectedXA = new BehaviorSubject<string>(null);
+    // xa$ = this.selectedXA.asObservable();
+
+    selectedXA: string;
+
+    changeXA(xa: string) {
+        this.selectedXA = xa;
+    }
+}