Add spanish as an example

Adding a new language without nlp requires now only to fill out the
pieces:

- define a list of month names to support date recognition
- add it to joex' dockerfile to be available for tesseract
- update the solr migration/field definitions
- update the elm file so it shows up on the client

docker/joex-base.dockerfile

@@ -16,6 +16,7 @@ RUN apk add --no-cache openjdk11-jre \
     tesseract-ocr-data-deu \
     tesseract-ocr-data-fra \
     tesseract-ocr-data-ita \
+    tesseract-ocr-data-spa \
     unpaper \
     wkhtmltopdf \
     libreoffice \