Adapting to new ly.music design for durations

The duration node is now placed as a child in the tree structure, but only if it's present in the source code.

The duration type etc of the current note is now set with the value of the last note and changed afterwards if a duration child is found.
Unfold repeats directly
Clear ly dependency earlier

Keep object structure MusicXML generic.
More adjustments to the object structure
Adjustment to rest with position
Use copy function instead
Adjustments for chords
Reference pitch must be absolute
midiinput: more robust unloading
More cleaning up of the duration code
Preserve numerator and denominator for scaler elements
Create the new bar first when multiplying rests
Merge pull request #507 from PeterBjuhr/musicxml

Musicxml Export wip
Merge pull request #505 from mamoch/master

midiinput: more robust unloading
dont try to load non-existent file when traversing an included file
fix remote with argparse
Updated french translation
Merge pull request #510 from rdoursenaud/french

Updated french translation
Update ChangeLog