Change
var app = angular.module('app', ['ngRoute'] );
to
var app = angular.module('app');
in your controllers and everything will be fine
By adding second argument to the module function you register new module.
Updated your plunk
Update
About contact view. There is another typo:
templateURL: 'contact.html'
and should be:
templateUrl: 'contact.html'
Plunk updated.