Add sigel to data

[acka47]

We right now have to map sigel to ISIL in hbz/lobid-resources#907. If others have to do similar things it would be good to have sigel in lobid-organisations to look up the corresponding ISIL easily.

The sigel is in 008H, subfield d see e.g. https://services.dnb.de/sru/bib?operation=searchRetrieve&query=isl%3DDE-605&recordSchema=PicaPlus-xml&version=1.1:

<ppxml:tag id="008H" occ="">
  <ppxml:subf id="b">ZY571</ppxml:subf>
  <ppxml:subf id="d">605</ppxml:subf>
  <ppxml:subf id="e">DE-605</ppxml:subf>
</ppxml:tag>

[TobiasNx]

see here: http://test.lobid.org/organisations/DE-605.json

"sigel": "605",

We should add this to the GUI, too.

[acka47]

+1

We should add this to the GUI, too.

I am not sure we need this. For me it's ok to only have it in the JSON for now.

[TobiasNx]

see here: http://lobid.org/organisations/DE-605.json

"sigel": "605",

deployed with #450