Need to remove $$hashKey property on objects to store in MongoDB

AngularJS adds $$hashKey property on objects listed in a ng-repeat directive.
When we use $resource, $http or angular.toJson AngularJS removes this transient property but when we use Meteor insert this property is not removed and it failed on MongoDB insert with this error :
at _Mongo.insert (app/packages/mongo-livedata/mongo_driver.js:172:8)
Exception while invoking method '/annonces/insert' Error: key $$hashKey must not start with '$

The fix must be recursive on the object properties to insert.

See merge request #28