Progress on QweakGeant4 (visualized with Coin3D)

- included the MiniTorus magnetic field and coils
- included the coils of the main magnet. Somehow there is a visualization bug in the coils which are made out of a
  boolean Union of plates and disks with holes (affects Coin3D and VRML)
- Changed und upgraded QWeakSimShieldingWall into QweakSimCollimator
  Instances are now the 3 collimators and the shielding wall, the octant cutouts can be trapezoids (ShieldingWall)
  or cones (Collimators).
  Have not figured out how to change the geometry of a boolean volume between runs (myRun.mac).
  (geometry has to be deleted and rebuild from scratch, but certain pointers get lost)
  At present the collimator geometries are customized within QweakSimDetectorConstruction (e,g, colli->SetInnerRadius)
- the magnetic fields (QTOR and MiniTorus) are defined as local fields bound to a local volume. So when I move a magnet
  (esp. the MiniTorus), the field will follow automatically.
  However the field map of the MiniTorus is defined for a huge volume.

- To be done: Collimator volumes have to be inserted into the MiniTorus volume rather than into the MotherVolume
  (due to field map range).