closes#7688
- Use `/favicon.ico` and `/favicon.png` in blog app. Depending on type of storage (custom upload = local file storage), serves either from storage adapter with `read()` method or reads the bytes via `fs`.
- Redirects requests for `favicon.ico` to `favicon.png` if custom `png` icon is uploaded and vice versa.
- Redirect requests for `favicon.png` to `favicon.ico` if default icon is used (in `core/shared`).
- Changes the `{{asset}}` helper for favicon to not serve from theme assets anymore. It will either be served the custom blog-icon or the default one.
- The `{{@blog.icon}}` helper renders the url of the **uploaded** blog icon. It won't render the default icon.
