Change data store to parse documents to extract titles

[marcpalmer]

The current mechanism is bad - the name is not editable, the filename is deduced from the title and then used as the title which cannot be seen again.

Solution: just load all the files, use their filesnames as filename, parse YAML or JSON for the title.

When creating, make a new filename from the title.

When updating, if title changed, save with new name and delete old name and rename old attachment.