Saving storage. Moving from TVector3 to ROOT::Math::XYZVector

[jgalan]

We are now using TVector3 data members inside axionlib, however following ROOT pages this class is now obsolete, and the TVector3components are built using Double_t type.

https://root.cern.ch/doc/master/classTVector3.html

They propose to move towards ROOT::Math::XYZVector that can take the form of Float_t type using ROOT::Math::XYZVectorF.

We should update mainy the dadtamembers inside TRestAxionEvent and update rotation and vector operations everywhere where they are used.

Also, the observables could be made float type, just by doing SetObservableValue( "obsName", (Float_t) value );.

Saving space should be also possible by dropping the event data. See issue: rest-for-physics/framework#507