GRSciColl - add checkbox to select primary identifier

[ManonGros]

Now that the back end has been implemented (gbif/registry#625), I would like to make it possible for editors to choose a primary identifier. Maybe with a checkbox in the identifier window like we have for contacts? (see below)

What we currently have for contacts:

Where I imagine the checkbox would be for identifiers:

See also this issue on displaying identifiers in the GRSciColl website: gbif/hp-grscicoll#158