* ScanSaving objects can have a name to store data in redis, if no name
is given an unique identifier is generated
* ScanSaving: added 'scan_number' and 'scan_number_format', removed 'run_number'
* ScanSaving: removed 'scan' key replaced by 'scan_name'
* added 'data_path' to dict returned by ScanSaving.get()
* Scan: changed constructor signature, "parent", "writer" has to be
passed through a ScanSaving object, if no object is specified the default
ScanSaving object for the session is used. Added "save" flags.