Tools: Magnetic field tool.

Currently Plots:

1. Bz
2. B_parallel (to the ray)
3. B_perp (to the ray)

Will build flexible command line args.

Idea: Add the same tool but for integrated radiation length along the ray.

examples/gem_tracker_disc.xml

@@ -119,15 +119,6 @@
 
   <detectors>
 
-    <detector name="BeamPipe" type="BeamPipe" vis="GrayVis" >
-      <component material="Aluminum" length="CentralBeamPipe_length" 
-        thickness="CentralBeamPipe_thickness" radius="CentralBeamPipe_radius" z="CentralBeamPipe_z" />
-      <component material="Aluminum" length="UpStreamBeamPipe_length" 
-        thickness="UpStreamBeamPipe_thickness" radius="UpStreamBeamPipe_radius" z="UpStreamBeamPipe_z" />
-      <component material="Aluminum" length="DownStreamBeamPipe_length"
-        thickness="DownStreamBeamPipe_thickness" radius="DownStreamBeamPipe_radius" z="DownStreamBeamPipe_z" />
-    </detector>
-
 
     <!--
     <detector id="2" name="GEMTracker_PVDIS" vis="RedVis" type="GEMTrackerDiscSOLID" readout="GEMTrackerHits" >