Remove height 100% from horizontal thumnbail and align

Height 100% makes the thumnbail to big and stretches the image outside it's container. This clips the image and also oversizes it which results in a pixelated image.

Author: Nick de Kleijn

lib/web/mage/gallery/gallery.less

@@ -697,8 +697,8 @@
     }
     .fotorama_horizontal_ratio {
         .fotorama__img {
-            .translateX(-50%);
-            height: 100%;
+            .translate(-50%, -50%);
+            top: 50%;
             left: 50%;
             position: absolute;
             width: auto;