refractor: core module (#289)

* Shift services into their own folders.
* Add comments.

Fixes #288

src/app/core/alert/alert.model.ts

@@ -0,0 +1,7 @@
+/**
+ * Alert model.
+ */
+export interface Alert {
+  type: string;
+  message: string;
+}

src/app/core/alert/alert.service.spec.ts

@@ -0,0 +1,15 @@
+import { TestBed, inject } from '@angular/core/testing';
+
+import { AlertService } from './alert.service';
+
+describe('AlertService', () => {
+  beforeEach(() => {
+    TestBed.configureTestingModule({
+      providers: [AlertService]
+    });
+  });
+
+  it('should be created', inject([AlertService], (service: AlertService) => {
+    expect(service).toBeTruthy();
+  }));
+});

src/app/core/alert/alert.service.ts

@@ -0,0 +1,33 @@
+/** Angular Imports */
+import { Injectable, EventEmitter } from '@angular/core';
+
+/** Custom Model */
+import { Alert } from './alert.model';
+
+/**
+ * Alert service.
+ */
+@Injectable({
+  providedIn: 'root'
+})
+export class AlertService {
+
+  /** Alert event. */
+  public alertEvent: EventEmitter<Alert>;
+
+  /**
+   * Initializes alert event.
+   */
+  constructor() {
+    this.alertEvent = new EventEmitter();
+  }
+
+  /**
+   * Emits an alert event.
+   * @param {Alert} alertEvent Alert event.
+   */
+  alert(alertEvent: Alert) {
+    this.alertEvent.emit(alertEvent);
+  }
+
+}