Set class to image widget

issue10562
review369251002

src/sao.less

@@ -692,12 +692,6 @@ img.icon {
             margin-bottom: 5px;
         }
     }
-    .form-image_ {
-        img {
-            width: 4em;
-            height: 4em;
-        }
-    }
     .form-document {
         object {
             object-fit: scale-down;

src/view/form.js

@@ -1069,7 +1069,7 @@ function eval_pyson(value){
         init: function(attributes) {
             Sao.View.Form.Image_._super.init.call(this, attributes);
             this.el = jQuery('<div/>', {
-                'class_': this.class_
+                'class': this.class_
             });
             this.img = jQuery('<img/>', {
                 'class': 'center-block',