[FIX] web_editor: properly save a t-field in a t-ignore environment

When a t-field element was in an editable t-ignore environement,
modifying it was leaving the edit mode style attached to it. This
was because of:
1) When the t-field element was changed, it was marked dirty but
   also its parent editable container. Fixing this, only solves
   the case where only the t-field (and not one of its neighbors)
   is changed but it was worth fixing anyway.
2) Before saving an element, the potential 'o_editable' and
   summernote classes were not removed of its descendant and were
   thus saved.

Bug found with task-38069, merged in stable as it might occur there
too.

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

@@ -330,10 +330,11 @@ var RTE = Widget.extend({
         });
 
         // start element observation
-        $(document).on('content_changed', '.o_editable', function (event) {
+        $(document).on('content_changed', '.o_editable', function (ev) {
             self.trigger('change', this);
-            if(!$(this).hasClass('o_dirty')) {
+            if (!ev.__isDirtyHandled) {
                 $(this).addClass('o_dirty');
+                ev.__isDirtyHandled = true;
             }
         });
 
@@ -366,6 +367,10 @@ var RTE = Widget.extend({
 
         var editables = history.getEditableHasUndo();
 
+        $('.o_editable')
+            .destroy()
+            .removeClass('o_editable o_is_inline_editable');
+
         var defs = $('.o_dirty')
             .removeAttr('contentEditable')
             .removeClass('o_dirty oe_carlos_danger o_is_inline_editable')