TextLocator/implement literature search

[warm-coolguy]

Summary

• Implemented document search, that is, the AddressSearch bar now also offers results for documents, and clicking on one will retrieve a list of toponyms from the backend and resolve them against the gazetteer. Previously, we had a "get all documents regarding place" functionality. Now, a "get all places regarding document" feature is implemented.
• Additionally to the AddressSearch, this can be triggered on documents found in the previously implemented way; the "get all places regarding document" functionality is available from within the GeoSearch result display with one of the right-hand buttons.
• The backend API changed. The changes have been adapted to.
• The "heatmap" feature is currently not working. This will be adressed in a follow-up PR. For now, the feature correctly zooms, but the map stays cold. (https://github.com/Dataport/polar/pull/195)
• The result display may become confusing due to a growing number of ways to fill in the contents. To address this issue, further context information ("How did I get this result?") will be added in a separate PR. (https://github.com/Dataport/polar/pull/194)

Instructions for local reproduction and review

npm run textLocator:dev

• Test new search features.
  • (AddressSearch) Try searching for "Marine" and clicking the first literature result. (Other results may not yield toponyms relevant to the used gazetteer.) (Edit: Meanwhile, wildcard has been implemented. Also search for "Marin" to see if it works; should yield results now.)
  • (GeoSearch) Click into the map, e.g. on Neuwerk. In the result section, when having "Text" as sorting order, click the magnifying glass icon to load all geometries regarding any text.
• Since the backend API was changed and everything required touching, testing everything across the board seems to be in order. Exceptions have been noted in the Summary.