dc_tree_widget._loaded_sample_item is None if no Sample is
currently loaded
Accessing the model through the method get_model instead of .data
Adapting the EnergyScan hardware object to the new queue.
Improving the EnergyScanQueueEntry by adding handlers for
the callbacks/signals called/emitted by the EnergyScan HO.
Submodule update,

Logging operator messages to the user_level_log as well.