a global instance of ScanSaving to be available as SCAN_SAVING
current _ScanDataCallbackfor standard step scans to be renamed StepScanDataCallback
refactoring Scan class constructor: make a merge with class ScanRecorder ; so ScanRecorder will disappear. There is no default for writer or scan_data_callback, but we provide 2 functions instead: step_scan(...) that returns a ready-to-use Scan object for a step scan. Scan will have the following signature: (chain, name='scan', parent=None, scan_info=None, writer=None, data_callback=None) ; if scan_info is None it has to be initialized as an empty dict ({}).
if writer is set to None in Scan, it means "no saving"
remove _DataManager, DM singleton, etc (relic of ancient code)
standard scans: extra_counters to be renamed counters, either a list of counters is provided for the scans OR a measurement group; if nothing is specified, current active measurement group is used
remove one_shot from all Acquisition devices (masters and slaves), it is replaced by a stopper flag on the DeviceIterator object
AcquisitionChain wins a new method set_stopper(dev, boolean) to set the stopper flag manually, otherwise this flag is set automatically on the DeviceIteratorobject when executing the scan