Allow ingest and editing of line-level annotations (#1504)

[blms]

In this PR

Per #1504:

• Parse the line geometry and metadata in eScriptorium output ALTO XML to create individual annotations per line
• Use the textGranularity property to indicate block- or line-level annotation granularity, and a new foreign-key relation between Annotations to represent relationships between the two
  • Update HTML serializer to iterate over only block-level annotations, and if they have associated line-level annotations, compile those lines' contents into an ordered list
• Pass a “line mode” parameter to Tahqiq to tell it when to switch to line-level functionality

see also https://github.com/Princeton-CDH/annotorious-tahqiq/pull/31

Notes and questions

• Is partOf a good field name for the associated block's ID in a line-level annotation? It’s not standard W3C, as that field name typically refers to an AnnotationCollection that an AnnotationPage is part of, but not sure how else to indicate in the serializer what the associated block should be for a line.
• I tried to keep it flexible enough that textGranularity could remain null for normal (block-level) annotations, to avoid having to update code everywhere annotations are created/parsed/etc. Also avoids having to write a data migration to add block granularity to all existing annotations.

[codecov[bot]]

Codecov Report

Merging #1537 (0434bdd) into develop (a18ae8b) will increase coverage by 0.20%. Report is 52 commits behind head on develop. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #1537 +/- ## =========================================== + Coverage 98.43% 98.64% +0.20% =========================================== Files 219 227 +8 Lines 12329 14217 +1888 =========================================== + Hits 12136 14024 +1888 Misses 193 193 ```

[blms]

Good call @rlskoeser, the exports work fine as they just call the same methods content_html and content_text that we use in the public site. However, the filenames were showing up as unknown-author, so I went ahead and fixed that and added a test for it. Merging as soon as checks pass—thanks for the review!