Allow geometry material selection from rml #108
Description
After talking with @cmargalejo offline we thought it might be a good idea to be able to modify the sensitive volume material from an RML (use xenon instead of argon, etc.). This could apply to any volume.
I guess the appropiate place to handle this would be the detector section, we could have something like:
<detector>
<volume name="gasVolume" sensitive="true" maxStepSize="0.05mm" material="NewMaterial"/>
</detector>
The material would then be replaced in the gdml and all required additions to the <materials/> tag would also be automatically made. The new material could be available in the gdml already or we could use the default materials file.