Added the Tree Header classes to the framework.
Added the Tree Header classes to the framework.

JPETTomography/j-pet-framework-examples,wkrzemien/j-pet-framework-examples,JPETTomography/j-pet-framework-examples,JPETTomography/j-pet-framework-examples,wkrzemien/j-pet-framework-examples,JPETTomography/j-pet-framework-examples,wkrzemien/j-pet-framework-examples