Remove the dependency of TrackBase on Geant3

[YanzhaoW]

Is your feature request related to a problem? Please describe.

Hi,

I am installing FairSoft without Geant3 library and found out that the TrackBase in FairRoot would not compile if Geant3 doesn't exist:

FairRoot/fairroot/CMakeLists.txt

Lines 32 to 35 in b3a0a26

	if(Geant3_FOUND)
	add_subdirectory(geane)
	add_subdirectory(trackbase)
	endIf()

But looking at the trackbase/CMakeLists.txt, I didn't find any explicit dependencies on Geant3 from TrackBase library.

Would it be possible to compile TrackBase even if Geant3 doesn't exist?