Revision of menu alignment, to include 0-multiplicity chains

To include the Anomaly-detection chains with chains that involve multiple signatures all together, we found conflicts due to multiple Empty sequences with the same name added in different steps during the alignment. I made some debugging and made these changes:

• increased debug details and documentation
• new function getMergedEmptyStepName() to unify the way the empty steps are named (when created in different conditions they ended-up with different names)
• in makeCombinedStep() correct the leg numbering to give the correct name to the empty sequences
• removed useless use of step multiplicity in the empty steps name (harmless)
• in Chain.numberAllSteps(), modify the empty sequences name when the steps are aligned, to follow the same name change of the steps

Tagging @tamartin, @khoo and @ksugizak