Added image preloading & smooth image transition + bug fixes

block_product_details.php:
1437-1442     - image URL variables
1591-1594     - assigning the variable values
1704-1707     - adding images to the template

block_product_details.html:
16-32     - removing images.js script; made scripts async; added "var"s;
pre-loading big images (24); showBigImage function with smooth
transitions;
40     - "read more" animation bug fix / improvement - for short
descriptions the height set to be automatic;
212-225     - image div rearaingement for animation + (vertical)
centering of the images;

general.css:
social button positioning and "read more" button styles.