Add support resize option

set resize="<width>,<height>" in the field tag definition to
make the server return a resized version of the image.
Useful for saving bandwidth when dealing with large images and to
have uniform image sizes (aspect ratio is mantained by filling
emtpy areas with transparent background)

web_tree_image/static/src/js/web_tree_image.js

@@ -35,7 +35,15 @@ openerp.web_tree_image = function (instance) {
                     // The media subtype (png) seems to be arbitrary
                     src = "data:image/png;base64," + value;
                 } else {
-                    src = instance.session.url('/web/binary/image', {model: options.model, field: this.id, id: options.id});
+                    var imageArgs = {
+                        model: options.model,
+                        field: this.id,
+                        id: options.id
+                    }
+                    if (this.resize) {
+                        imageArgs.resize = this.resize;
+                    }
+                    src = instance.session.url('/web/binary/image', imageArgs);
                 }
             } else {
                 if (!/\//.test(row_data[this.id].value)) {