POST Forms: Nonce fields according to current action

[nicolas-jaussaud]

Hi @zinigor!

As I mentioned in this comment on a previous pull request, I think we need to update the way we handle nonces

This pull request does the following changes:

• Move get_nonce_action() from UrlBuilder to DataViewConfig
• In the default layout, display action buttons according to current action
• Switch from the default input name for nonces (_wpnonce) to use an action specific one (_wpnonce_{action}))

The reason I moved get_nonce_action() away from UrlBuilder is because we also use it to generate nonce fields in our POST <form>, and as it relies on get_menu_page() to generate the nonce action name I thought it could make sense to move it to DataViewConfig (honestly wasn't really sure what would be the best place)

The default layout was returning a "Save" and "Delete" button for the create action, we should now display only a "Create" button instead

Lastly, it switch from the default name for the nonce field (_wpnonce) to an action specific name. It was causing issues in the edit form, as we need a 2 nonce fields (2 actions in the same form: edit and delete). Both actions require a different nonce in the backend (here and here), so we have to use a different name otherwise the second nonce will overwrite the first one

[zinigor]

Looks good to me!