Child revisions for devices need to be cleaned up from memory

When a device is created, a node is created within the data model to hold information for that device and is then saved a a child at the root of the model.  When an update is made to that device, a new child revision is stored at the root.  The previous revision should be discarded.  Unfortunately, the current implementation does not properly discard old revisions from memory, which will have an impact on the overall performance of the system when increasing the load.