fix(ga): expose ga settings in ga provider #87 (#281)

- **What kind of change does this PR introduce?**
* Add a feature to the ga provider.
- **What is the current behavior? Link to open issue?**
* No way to set `additionalAccountNames` on `settings` config object. #87 
- **What is the new behavior?**
* A new method in the google analytics provider that allows a user to set a list of additional account names. These account names are used in any subsequent tracking events, exceptions, etc.

closes #87

src/lib/providers/ga/ga.spec.ts

@@ -198,4 +198,14 @@ describe('Angulartics2GoogleAnalytics', () => {
     ),
   );
 
+  it('should allow modification of GA specific settings',
+    fakeAsync(inject([Angulartics2, Angulartics2GoogleAnalytics],
+      (angulartics2: Angulartics2, angulartics2GoogleAnalytics: Angulartics2GoogleAnalytics) => {
+        const additionalAccountNames: string[] = ['additionalAccountNameOne', 'additionalAccountNameTwo'];
+        angulartics2GoogleAnalytics.settings.additionalAccountNames = additionalAccountNames;
+        expect(angulartics2.settings.ga.additionalAccountNames).toEqual(additionalAccountNames);
+      }),
+    ),
+  );
+
 });

src/lib/providers/ga/ga.ts

@@ -21,6 +21,7 @@ export class GoogleAnalyticsDefaults implements GoogleAnalyticsSettings {
 @Injectable({ providedIn: 'root' })
 export class Angulartics2GoogleAnalytics {
   dimensionsAndMetrics = [];
+  settings: Partial<GoogleAnalyticsSettings>;
 
   constructor(private angulartics2: Angulartics2) {
     const defaults = new GoogleAnalyticsDefaults();
@@ -29,6 +30,7 @@ export class Angulartics2GoogleAnalytics {
       ...defaults,
       ...this.angulartics2.settings.ga,
     };
+    this.settings = this.angulartics2.settings.ga;
     this.angulartics2.setUsername.subscribe((x: string) => this.setUsername(x));
     this.angulartics2.setUserProperties.subscribe(x => this.setUserProperties(x));
   }