Interpretation labels all live at the same layer

Previous to this commit, we had interpretations of paragraphs ("999-Interpretations-22-(a)(3)(v)(Q)"), as well as of whole sections ("888-Interpretations-44") and appendices ("554-Interpretations-R").

This is a problem as interpretations are composed of paragraphs of varying depth, hence we'd see things like "777-Interpretations-23-3", i.e. the third paragraph of the interpretation of section 23. Note that this conflicts with "777-Interpretations-23-(a)", which is *not* an interpretation paragraph.

This pull requests standardizes on [Part, "Interpretations", Label] + InterpretationParagraphs. The two examples above become "777-Interpretations-23-3" and "777-Interpretations-23(a)", with the third element describing the paragraph we are interpreting and all elements after the third indicating paragraphs of the interpretation.