Fixed asynchronous publishing  handling

> Fixes EZP-22641
> Status: doing to dos
> BC note: ezsystems/ezpublish-legacy#941

Enables asynchronous publishing in `ezmultiupload/upload`.

Changes display of published items to use content_view_gui instead of node_view_gui, so that unpublished content is properly displayed.

Introduces a minor BC break since existing overrides of `node/view/line_thumbnail.tpl` will have to be updated to override `content/view/line_thumbnail.tpl`.

### TODO
- [x] Add `content/view/line_thumbnail.tpl`
- [ ] When backporting, don't delete `node/view/thumbnail.tpl` overrides (`.tpl` + `override.ini`)