add-file: Add chapter, book and part options

[erinendrei]

After reviewing the manual, especially 7.1.5.1, it seemed to make most sense to add both book and part alongside chapter. I know that it varies quite a lot which epub:type is associated with book: it can be division, part, or even chapter; but the templates are always going to need to be edited further by the producer anyway, so I don't think this undermines the utility of being able to quickly generate the basic skeleton with the add-file command.

If you don't think all three of these options are useful, let me know which you want excluded.

Also, contrary to what I said in the issue, it does seem necessary to have a chapter template for this purpose that is distinct from the one used by split-file. Let me know if you disagree about that, or anything else here, and I'll make the necessary changes.

I also noticed a typo in a function name in add-file.py: _replace_languague should be _replace_language. It doesn't affect any functionality because the typo appears throughout. I'll wait until this is merged or closed to fix that in a separate PR.

resolves #1006

[apasel422]

Do the new options need to be added to the shell completions?

[acabal]

Thanks Erin! As Andrew noted, we also need to add shell completions.

I don't think it makes sense to add both book and part, because the structures are almost identical. Just part will do and the producer can tweak it to fit. I would also remove data-parent, that can be added by the producer if necessary.

The ID should just be part-1. In the chapter, its ID should also just be chapter-1 with no data-parent. Chapter Title must also be a placeholder.

[erinendrei]

Thanks Andrew and Alex; sorry I missed that. All the changes mentioned should be there now, as well as two others: the xml:lang attribute in the chapter template is now LANG instead of en-US, and alphabetical order in add-file.py reinstated.

[acabal]

Great, thanks!