Improvement in signatures

- A Signature can now be saved with Signature.save()
- A signature has now a cutoff attribute

- add a list of build graph attribute in Layout lblyg
- smart layout.dumpr() and layout.dumpw() methods (save build graphs)
- add Layout.cy2pt to obtain a point ( nd array) in a given cycle

- add in project dir
output/sig
output/r2d
output/r3d

bugfix
- restore mulcplot