Left arrow shown when first image clicked

[bob-lee]

Nice work, found minor thing: when first image clicked, left arrow is shown wrongly as updateArrowActivation() is not being called. Suggest replace updateArrowActivation() with two getters like:

public get left(): boolean {
return this.currentIdx > 0;
}

public get right(): boolean {
return this.currentIdx < this.images.length - 1;
}

Then in template:

<img [ngClass]="{'activeArrow': left}" ... />
<img [ngClass]="{'activeArrow': right}" ... />

[BenjaminBrandmeier]

Thanks a lot @bob-lee!
Included your suggestion in the code, just with different method naming.

If you'd like to contribute more, I'm also happy to accept pull requests.