Added option to use TIGRESS positions

Added code to use TIGRESS detector positions rather than GRIFFIN. Use
this command BEFORE using the "add GRIFFIN detector" commands.
/DetSys/det/UseTIGRESSPositions true
Added "stepTracker" output

This new functionality outputs step information (event#, step#, det#,
cry#, pos, etc) to a root tuple tree. To activate this code set
stepTrackerBool = true; at the top of EventAction.cc. It is currently
set to false because outputting all this information is computationally
expensive. We don't want to do it unless we need it.
Merge pull request #44 from evan012345/master

TIGRESS positions and "stepTracker"