+ Update trapezoid geometry for gaspard

  - A specific bug was present in ThinSi.cc : deletion of the material
    (forbidden)
  - A general bug was present causing the TTree to crash: The branches
    address need to be cleared and the branches deleted before
    reloading the geometry

  - Reload the current generator
  - Load a different one
  - Adding corresponding button in the GUI

 - Delete the actual geometry
 - Clear the Detector Manager
 - Reload Geometry file

For this to work a couple of thing has been done:
 - InitializeRootInput now need an extra SetBranchAddress to tell the
   tree that the previous address is no longer in use
 - Scorer can not be cleared, so need to be retrieved in case of a
   reloading. If they do not exist they are created
 - This is done using the new CheckScorer static method from VDetector