* make previewer use a more generic Adapter to flip through cards;
* return Previewer from `show_preview()` for testing,
* as well as Edit dialog from `open_dialog_and_show_note_with_id`;
* disable/enable `Edit` editor buttons more reliably;
* a few minor changes
Like Edit Current, but:
* has a Preview button to preview all cards for this note
* has a Browse button to open the browser with these
* has Previous/Back buttons to navigate the history of the dialog
* has no Close button bar