- add a file selector to load a new HDF5 file
- add JPEG and PNG viewer widget (plugin)
- add object information: type, number of attributes, path (e.g. /versions/format_version)
- add hex viewer widget
- add markdown viewer for datasets that contain markdown text (maybe leave this as a plugin?)
- configuration options, e.g. which plugins to use/enable
- add a help screen and also a --help app argument