Fix metadataselector sort
This is a set of of small changes to the metadata selector widget:
- Sort the list
This seems a reasonable thing, especially as the XMP list is longer now, since adding missing namespaces.
- Allow the child indicator to be visible
I've often wanted to be able to collapse the views, but had no idea that double-clicking the header does that. I'm sure I'm not alone. I think it would help new users to make this more visible. I realise the look needs improving, and I plan to do this, but it will require separating the MdKeyListViewItem class which is shared with the RHS panel metadata widget.
- Add a tooltip to the tag item rows
This shows the full Exiv2 style name ("family.group.tag"). I though this would be helpful to technical users who understand metadata and use the exiftool and exiv2 CLI tools.
- Wrap columns at 80, and tidy some of the comments
Just to make the code a little easier to read for the next person who comes along.