declare dependents objects to their reference (to be able to remove the reference without error)

- move the maxlen attribute to OE_stitch class with a stitcchMaxLen funct (every child class can use it)
- add a defaultLinkMaxLen for the linkstitch class
- remove start and end attribute in linestitch (subcurve class make them obsolete)
- add get functions for curves in OE_controller class

add a new subcurve class (parametric subcurve) and a joincurve (concatenate curves)

a linkstitch is created automaticaly in the controler before every new stitch
- add a refreshStitchs function to the controler to refresh all the stitchs of the document

add thread class (stitch one, not computing) to deal with color, width and later (maybe) rendering style

second move to a MVC design

add a OE_svgParser class to fill the document
first move to a MVC design