Display updates for manuscripts with multiple levels of msPart

[wlpotter]

Example record: https://bl.syriac.uk/ms/106 (part 1 has 1.1 and 1.2, not displayed currently). In some cases (e.g., where only part of a manuscript is palimpsest) we've created two levels of tei:msPart elements. These are currently not displaying. The attached mockup shows how they should be displayed. Mockup: https://docs.google.com/drawings/d/10BUnElLVTQNthLMe8h7YoWuKyy8A5IfyH6nV5H_LpWQ/edit?usp=sharing

Each sub-part will have the full description elements (overview section, physical description, contents, additions) that should be nested within the bounding box of its containing msPart. However, the containing msPart may itself have information in the overview and physical description sections, so we will want to clearly delineate the two

As well, the table of contents at the top of the page should be updated to include this second level of part, with indented entries for the sub-parts (i.e., 1.1 1.2 etc.), as in the following screenshot:

The anchor targets should use the msPart/@xml:id values, in keeping with the other msParts in the TOC. The 1.1, 1.2 can either use document order or the msPart/@n attribute values

[wlpotter]

FYI @wsalesky we briefly touched on this in December, but here is a mockup and example record for the cases in SMBL where we have two levels of msParts. We can go over it more next week when we meet

It looks like we do have one case (https://bl.syriac.uk/ms/872, part 3) where we nest to three levels. That might not be worth the trouble though, so we should discuss