Modifications for G4 simulation:

Modifications for G4 simulation:
- Move call to detector->CreateMaterials() from AliMC::Init()
    in AliMC::ConstructOpGeometry(); as materials have to be defined
    when we set optical properties
- In EMCAL, HMPID:
    Move definition of cuts and process controls per tracking media
    in Init()
- In AliStack:
    Set fCurrentTrack in functions called by Geant4:
    PopPrimaryForTracking(), SetCurrentTrack()
Updated G4 macros:
- Extended g4menu.C with buttons for running in batch
    and running G3 simulation
- Updated magnetic field
- Changed the default physics list selection to QGSP_BERT_EMV+optical;
    removed specialControls from selection
- Set default range cut value to 0.01 mm
- Added commented line with Geant4 VMC commands useful for
    debugging

(I. Hrivnacova)