Separate out application and shape metadata

[kltm]

From discussion earlier today, there is some application specific metadata in the json-export branch, where @tmushayahama is working on JSON for the form. The kind of things we want to separate out are fields like "weight", "box label", "title label"...

As part of this discussion, since the metadata is required for several sub-parts of Noctua, this could be incorporated in a new repo ("noctua-metadata" from the slack discussion), with the form metadata in a subfolder and a README.md explaining the contents at the top level.