Numerical Source + Optics Plane

At a glance

We have introduced SourceVirtual, SourceWavefront and OpticsPlane.

OpticsPlane should be (but still it is not) the superclass of classes like MirrorPlane, Detector, Slits.
For the moment, it is just the superclass of SourceWavefront.

Other Changes

• Behavior of Propagation Mediator (added the exception of SourceVirtual)
• Added property Lambda to BeamlineElements (to handle the different sources of the wavelenght)
• Renamed:
  AngleLab->AngleNormLab
  VersorLab->VersorNorm
  Still to clean AngleInputLabNominal
• Cleaned: OpticsNumerical

For the future

Subclass OpticsPlane for other things