added a fresnel whitefield reconstruction component.
The fine details of the routine are still to be ironed out. But this demonstrates
how we read data from the hdf5 file, pass it into the NADIA python bindings
to do the reconstructions and write the results back to the same data file.
Note, these changes rely on some changes made to the NADIA code and the python
bindings which are not yet committed, some of which may be best committed
to a branch rather than the main NADIA trunk.