Fix #149 Pinch zoom on IOS

[ryuuzake]

scale from iOS behaves differently between expo and native. When using expo, the scale value is between 0 and 1. But when using native, the scale value is above 1.

To solve this issue, I proposed to change the maxScale value to 3. The value 3 is suggested in #149.
from my testing, it actually doesn't matter to use what value as long as it's above 1

[ryuuzake]

@Hassan-Riaz I changes the code to pass the maxScale props from ImageViewing so now it's configurable. Because of it, I remove the maxScale logic in ImageItem.ios.tsx. Do we still need it? If so, I should add some kind of default logic.

[arjovanramshorst]

Is this going to be merged/released anytime soon? We are waiting on this functionality and patching the package does not seem like an optimal solution if the fix is here already.