[Halld-offline] PID library changes

[Paul Mattione]

After discussions with some of the other members of the offline group, I've made some minor changes to the PID library.  These changes are not yet checked into the main trunk, but for now are in the "sim-recon-pidchanges" branch of svn instead.  The main changes are:

 - "NeutralTrack" replaced with "NeutralParticle"
 - "NeutralShowerCandidate" replaced with "NeutralShower"
 - DChargedTrackHypothesis & DNeutralParticleHypothesis inherit from DKinematicData
 - Access functions were added to DChargedTrack and DNeutralParticle (e.g. Get_BestFOM(), Get_Proton(), Get_BestPhoton(), etc.)

These changes will break some of the programs and plugins until they are updated, so that's why they are in a separate branch.  Due to the large number of these, help would be appreciated in converting these packages.  When the fixes are complete, I'll merge them into the main svn branch.  Thanks. 

 - Paul