Add placeholder text to empty category pages
This commit adds a header to the Bookshelf which is shown if CategoryEntriesModel.count == 0. This occurs if e.g. there are no comics with the according metadata in the library.
This commit adds a header to the Bookshelf which is shown if CategoryEntriesModel.count == 0. This occurs if e.g. there are no comics with the according metadata in the library.