[FIX] web_editor: hide link buttons duplicates instead of removing them

For example, if primary = alpha, the primary button option is removed
in the link dialog. When editing a primary button, this lead to broken
behaviors. Hiding the button does the trick.

addons/web_editor/static/src/js/widgets/widgets.js

@@ -1466,7 +1466,7 @@ var LinkDialog = Dialog.extend({
                 var $btn = $(btn);
                 var color = $btn.css('background-color');
                 if (_.contains(colors, color)) {
-                    $btn.remove();
+                    $btn.hide(); // Not remove to be able to edit buttons with those styles
                 } else {
                     colors.push(color);
                 }