BugFix in pluto/PDataBase, fix of compiler warnings

@f.uhlig, @v.friese, please have a look.

I fixed small but annoing compiler warnings in few places in aliroot.

(It is maybe not my business. Initially, I wanted to fix KFParticle warnings and I did. Then I realized that KF is an external package that I can not modify from the cbmroot repository. Anyhow, while doing this I also fixed most of the other cbmroot warnings)

An important thing is that c++ compiler found a bug in pluto/PDataBase.cxx:

char* PDataBase::GetDescription()

returns a non-valid pointer to a temporary local variable.

I changed the return type to TString, please take a look and confirm that it is fine.