Replace :rest:0.7 plugin dependency with the REST Client Builder Plugin

[aruizca]

The rest plugin introduces some dodgy dependencies and it also has not been updated for more than a year. The REST Client Builder Plugin on the other hand has a better API and has been created by Graeme Rocher

[sbearcsiro]

FYI: like a lot of things in Grails, REST Client Builder can break other parts of the grails ecosystem, in this case it's json rendering. See https://jira.grails.org/browse/GRAILS-11801