replace EmptyMenuSequenceCfg with createEmptyMenuSequenceCfg

This a follow-up of the TMMT cleanup after the ca migration.

Removed EmptyMenuSequenceCfg() and use createEmptyMenuSequenceCfg() to create empty sequences in all places, in particular inside the signature code, so that that they can use ChainConfiguration.getStep() instead of creating the ChainStep directly (as it is suggested in the guidelines ).

createEmptyMenuSequenceCfg() allows to create an EmptySequence generator function with the same name as the sequence that it creates, so one can track down the origin of the sequence (that otherwise is simply called “EmptySequence”)