REST interface for contact@reception endpoints

[ThomasLocke]

A simple list of strings would do just fine, such as ['thomas@domain','foo@bar','22334455'].

[rostgaard]

See
https://github.com/Bitstackers/ServerStack/blob/master/lib/contact_server/router.dart#L79
https://github.com/Bitstackers/ServerStack/blob/master/lib/contact_server/router.dart#L80
For REST API syntax.