Update source info in designspaces if font info changes

[ryanbugden]

If UFO gets renamed or path changes, update

• Use fontInfoDidChange to update source info.
• Use fontDocumentWillSave and fontDocumentDidSave to see if the path changed, and then change it in the DS.

Check if DS is open. If so, change the value and update it in DSE UI. If not, write it to the file.