rename cosign -> copay throughout code

Also, "cosigners" becomes "copayers"

js/controllers/send.js

@@ -1,6 +1,6 @@
 'use strict';
 
-angular.module('cosign.send').controller('SendController',
+angular.module('copay.send').controller('SendController',
   function($scope, $rootScope, $location) {
     $scope.title = 'Send';
   });