fix some signal-slot issues

- change the way to make linestitch and birailstitch (trace only one segment by default, remove validation with "return" key)

- fix a pan problem (2 time slower than the mouse move)
- add a backgroundColor in displayStyle

- fix a pan problem (2 time slower than the mouse move)
- add a backgroundColor in displayStyle

- add OE_actionDelPointLinkStitch and make it work

- make linkStitches point pickable

- remove the OE_commandDisplay class (specific functions are merged in OE_diplay)

- add a lot of displayStyle variables

- remove some old test functions in OE_controller

- add OE_controller::getSelectionBoundingBox function
- rename "select" function to "picking" in OE_interfaceDisplay (more clear name)
- change selection mode into an editionState in OE_interfaceDisplay
- add scale method to curves and stitchs
- add ScaleSelection state and implement the scale selection actions and UI widget
- clean and comment OE_interfaceDisplay
- add BoundingBox::getCenter method
- add OE_display::screenToDocument method

- TODO write OE_actionScaleSelectedLineStitchWidth::scaleWidth and scaleLen methods

- add actions for moves
- add - operator to vector_2d class

- change the color and size of end subcurve

- fix problems on linestitch interactive creation

- add creations function
- change functions in joincurve class to insert new curves anywhere and remove them
- add an action to create and add a subcurve to a joincurve

- add editLastAction function to OE_controller to make possible "live modification"
- add OE_actionSetPointCurve and OE_actionMovePointCurve to OE_actionCurves
- add setPoint function to OE_pointcurve and change getPoint to use reference instead of pointer

- add unselection with "control" key

- improve selection mode to create only one action for each clic
- fix problem on delete of some stiches

- add the interfaceDisplay class that will drive all the user interface and the display->controller interactions

- add instructions class
- add hoop, pulse/mm and zero point in document

- draw controls only for the selected curves and stitchs

- fix a bug in birailstitch class (initialisation of len and maxlen variable was not set)
- add the display of a point at 0,0

second move to a MVC design