fix: displaying images (series) with different sizes causes the image…

[Zaid-Safadi]

… to be clipped #304

Solution 1: By default, don't create a "displayedArea" in the viewport object and let user provides one if needed. otherwise, the code will use the full image dimensions

Pros:

Cleanest (IMO), someone explicitly setting the displayedArea knows what they are doing and can reset it for new images if displayedArea should be different.
Cons:

Any code assuming the viewport.displayedArea is created by default and accessing directly (such as applying my workaround above) will break.

[Zaid-Safadi]

I have an example which I can clean up and add but unit-tests are provided