RecreateGDML should recreate directory structure too

[wdconinc]

Is your feature request related to a problem? Please describe.
Right now the functionality exists to recreate the GDML files from the ROOT files produced by remoll. This is very useful. However, the files are all created at a single level in the directory structure, meaning that they cannot be used right away for a new simulation. They first have to be copied into their directories again, which you have to find by parsing the files.

Describe the solution you'd like
I'd like to have the files appear in the original directory structure.

Describe alternatives you've considered
We could also modify the files as they are written to remove any references to directories, but that seems more complicated than recreating the directory structure.

[wdconinc]

Issue with implementing this: When someone says /remoll/geometry /home/user/git/remoll/geometry/moller2.gdml, how do we figure out at what level to start recreating dirs?