Don't show non-contactable people on API page

[henare]

e.g. http://planningalerts.writeit.ciudadanointeligente.org/en/manage/settings/api/

At the moment, AFAICT, the API page lists every one of the contacts in your instance as an example. However if they don't have an email address then they're actually not contactable (what does the API even do in this case?).

I think the API page should only show contactable people as examples of who you can write to.