[FIX] web_editor: make sure gallery images are editable

When added for the first time, they were not editable until the page
was saved.

addons/web_editor/static/src/js/rte.js

@@ -535,7 +535,6 @@ var RTE = Widget.extend({
         }
         if ($editable.length && (!this.$last || this.$last[0] !== $editable[0]) &&
                 ($target.closest('[contenteditable]').attr('contenteditable') || "").toLowerCase() !== 'false') {
-
             $editable.summernote(this.config($editable));
 
             $editable.data('NoteHistory', history);

addons/website/static/src/js/website.snippets.gallery.js

@@ -208,7 +208,7 @@ options.registry.gallery = options.Class.extend({
             $slideshow = $(qweb.render('website.gallery.slideshow', params));
         this.replace($slideshow);
         this.$target.find(".item img").each(function (index) {
-            $(this).attr('data-index', index).data('index', index);
+            $(this).attr({'data-index': index, 'contenteditable': true});
         });
         this.$target.css("height", Math.round(window.innerHeight*0.7));