feat(Events): Add onLoaded and onError output events on audio-track component

[proustibat]

Based on the onFinish event, it works on the same way. I needed to do something like that:

    <audio-track #audio *ngIf="myOnlyTrack" [track]="myOnlyTrack" (onLoaded)="onTrackLoaded($event)">
        <ion-item>
            <ion-thumbnail item-left>
                <audio-track-play dark [audioTrack]="audio"><ion-spinner></ion-spinner></audio-track-play>
            </ion-thumbnail>
        </ion-item>
    </audio-track>

[proustibat]

I think I fixed another bug:

fix(Stop): Fix stop method error and add toggleStop method Calling stop method caused error because it was not implemented in a class. Also added a toggleStop method to be called, useful when using streaming adress because user doesn't want to be paused.