Allow for concordances in addition to reconstructions

This allows us to present complete parts that are absent from Du Chemin's printings but present in other sources. We want them to function like reconstructions, but be listed separately under "Concordances".
This creates a global object that isn't a good practice, and also the name is way too generic for what it is.
For sure it must be under the meiView namespace object and I wouldn't mind it you could find a more specific/descriptive name too.