* new online search provider base class to share results from the
online request to all online search provider.
* simplified ROI.create methods.
* IcyCanvas :
  - mouseEnter, mouseExit and mouseWheelMoved event to Overlay.
  - added new shortcuts for ROI.
  - others minors changes.
* handle shortcuts (delete, Ctrl+C, Ctrl+V...) from ROI panel.
* added general ROI constructors.
* added ROIEllipse2D.setToFitCircle(..) method.