\cadenzaOn/Off should change behaviour of \bar and barchecks

[Urs Liska]

\cadenzaOn should set a flag in lymus2musxml.py. If this is on then

• No <time> attributes to measures are created
• New measures are not triggered when the measure is complete, but only when a \bar is printed or a barcheck is used.
• At the same time \bar is modified insofar as there is no check for mid-measure bars. Instead, always a new measure is triggered.