Pinch to zoom on background images / videos

[mzorz]

The flow should work like this:

1. add images, videos, slides, etc
2. once you land on the composer, by default pinch to zoom will work on the background image or video
   3. as soon as you add views, pinch will only work on the added views
   4. as soon as the added views are gone if you delete all of them, pinch to zoom on the background will work again.

[mzorz]

For the record - we ended up deciding not to pursue pinch to zoom on videos for now, as it entails a different amount of work defining the use case and planning for it.

In any case, leaving this link here as I found a library that may work for our needs in the future. https://github.com/devlucem/ZoomableVideo

[mzorz]

For the record; note nbr 2:

3. as soon as you add views, pinch will only work on the added views

We did not go ahead with this one, as per the note left in the description here:

Note: we didn't disable the pinch gesture detection as specified in the issue, because it felt it didn't bother the intent of dragging / pinching on added views at all for me. Let me know if we still want to be strict about that and I can follow the described behavior enabling it when no added views are present, and disabling it if any added views exist on the frame.