[Halld-offline] DTreeInterface

[Paul Mattione]

As suggested by Matt Shepherd, I have developed an interface to creating and filling ROOT TTrees in JANA.  This interface abstracts away all the nastiness of locking and sharing branch addresses between threads.  Examples can be found at:

1) In a plugin:
https://github.com/JeffersonLab/sim-recon/tree/master/src/plugins/monitoring/SC_Eff

2) In an analysis action (DCustomAction_TrackingEfficiency):
https://github.com/JeffersonLab/sim-recon/tree/master/src/plugins/Utilities/trackeff_missing

>From now on, for thread safety, please use this interface when filling trees in JANA.  The classes used are:

DTreeInterface.* and DTreeInterfaceObjects.h at:
https://github.com/JeffersonLab/sim-recon/tree/master/src/libraries/ANALYSIS/

Please be sure to delete the interface at the end of the program to ensure that the tree is saved and the file is closed.  

 - Paul