Use promises api for user-related backend calls

src/app/budgets/add-edit-budget/add-edit-budget.component.ts

@@ -57,7 +57,7 @@ export class AddEditBudgetComponent {
 
     // TODO: Implement a search box with suggestions to add users
     searchUsers(username: string) {
-        this.twigsService.getUsersByUsername(username).subscribe(users => {
+        this.twigsService.getUsersByUsername(username).then(users => {
             this.searchedUsers = users;
         });
     }

src/app/shared/twigs.http.service.ts

@@ -302,10 +302,8 @@ export class TwigsHttpService implements TwigsService {
     return this.request(url, HttpMethod.GET)
   }
 
-  getUsersByUsername(username: string): Observable<User[]> {
-    return new Observable(subscriber => {
-      subscriber.error("Not yet implemented")
-    });
+  getUsersByUsername(username: string): Promise<User[]> {
+    return Promise.reject("Not yet implemented")
   }
 
   private async request<T>(url: URL, method: HttpMethod, body?: any): Promise<T> {

src/app/shared/twigs.local.service.ts

@@ -311,15 +311,11 @@ export class TwigsLocalService implements TwigsService {
 
   // Users
   getProfile(id: string): Promise<User> {
-    return new Promise((resolve, reject) => {
-      reject("Not yet implemented")
-    });
+    return Promise.reject("Not yet implemented");
   }
 
-  getUsersByUsername(username: string): Observable<User[]> {
-    return new Observable(subscriber => {
-      subscriber.next(this.users.filter(user => user.username.indexOf(username) > -1 ));
-    });
+  getUsersByUsername(username: string): Promise<User[]> {
+    return Promise.resolve(this.users.filter(user => user.username.indexOf(username) > -1))
   }
 
   private updateValues(old: object, changes: object, keys: string[]) {

src/app/shared/twigs.service.ts

@@ -55,7 +55,7 @@ export interface TwigsService {
   deleteTransaction(id: string): Observable<void>;
 
   getProfile(id: string): Promise<User>;
-  getUsersByUsername(username: string): Observable<User[]>;
+  getUsersByUsername(username: string): Promise<User[]>;
 }
 
 export let TWIGS_SERVICE = new InjectionToken<TwigsService>('twigs.service');