Moved setScaledImageSrc function to proper place

setScaledImageSrc was hidden in an "If" statement. This is not a proper place for a function that leads to the main functionality. The position of important function inside if clause can mislead any future code analysis. The change is quite simple - get setScaledImageSrc return to variable and than check if this variable is true or false.
Adding isImageIsScalable method to replace long if-else in zoomImages

long list of if-else can be moved to another method to clear out zoomimages functionality. The purpose of the if-else is to verify that the image can be scaled. isImageIsScalable return true or false based on the conditions in the if-else.
Moved image changed functionality into setScaledImageSrc

zoomImages changed image attribute based on src change made in setScaledImageSrc. I've changed that and now setScaledImageSrc is making this change along with the src change. If we are already changing image attributes in setScaledImageSrc, let it change all image attributes.
Moving all functionality of image analysis into setScaledImageSrc

When we are looping through all the images, we need to decide if the images are suitable for scaling. If they arent loaded yet, or they are marked as lazy load, or maybe failed to load scaled src in the past. All those conditions are being stated in isImageIsScalable. isImageIsScalable was called in zoomImages function - in the looping of the images. But there is no need to do that. We can move isImageIsScalable function to setScaledImageSrc, Now setScaledImageSrc is the only function that is being called in the image looping. if isImageIsScalable returns false, setScaledImageSrc will not continue.