Metadata restructure

[varunghat]

Narrows the two wide InventoryID mapping files down to just what the aggregation pipeline actually uses, adds InventoryID-Filenames.csv and moves phoible-references.bib into mappings/ so all the metadata lives together. Based on the PHOIBLE re-design doc "metadata restructure" section

Changelog:

InventoryID-Bibtex.csv: 5 cols (InventoryID, BibtexKey, Source, Filename, URI) -> 2 cols (InventoryID, BibtexKey). Dropped 23 exact-duplicate rows. 3840 -> 3817 rows.
InventoryID-LanguageCodes.csv: 5 cols (InventoryID, ISO6393, Glottocode, LanguageName, Source) -> 3 cols (InventoryID, Glottocode, ISO6393).
InventoryID-Filenames.csv (new): 3 cols (InventoryID, Filename, URI) take from the wide Bibtex file. 3031 rows for 3020 InventoryIDs.
phoible-references.bib: moved from data/ to mappings/

Fixed the links to phoible-references.bib in 7 source READMEs that referenced it (EA, ER, PH, RA, SAPHON, SPA, UPSID).

Added mappings/README.md

Tested with creating fresh clone and generating phoible.csv. Preserves parity with current committed phoible.csv

Notes:

Current changes remove source and language from the rows, which reduce human readability but add better metadata structure.

[drammock]

@varunghat re: the removed mapping of InventoryID:LanguageName:Source (from InventoryID-LanguageCodes.csv): where does the pipeline get it from if not that CSV file?

@bambooforest probably one for you to review?

[varunghat]

@varunghat re: the removed mapping of InventoryID:LanguageName:Source (from InventoryID-LanguageCodes.csv): where does the pipeline get it from if not that CSV file?

@drammock "Source" is set in validate_data <- function(dataframe,source_id,...) in aggregation-helper-functions.R
Function called in aggregate-raw-data.R manually for each source

eg:
saphon_data <- validate_data(saphon_data, "saphon", debug=debug)

LanguageName is taken from each raw data file directly

eg:
saphon_data$LanguageName <- keep_first(saphon_data$LanguageName, split.on=" (")