[Edition] Verifying that the primary keys are published in WFS

[rldhont]

The primary keys have to be published in WFS to be used in edition even if these fields are not displayed.

[Gustry]

Linked to #451

[Gustry]

Sorry, reopening here.

Edition doesn't ask the primary key of the layer, so the PR #553 was not fixing this ticket.

See edition definitions : https://github.com/3liz/lizmap-plugin/blob/master/lizmap/definitions/edition.py

I guess, PK should always be in WFS : according to specifications in #451 AND edition AND popup enabled ?

[Gustry]

For editing capabilities, it should be fixed with d47ad97

[Gustry]

I guess I can close here, I have added the PK for editing capabilities @rldhont and @mdouchin