netCDF file loading function

This function adds the ability to load netCDF files into python for further analysis using our analysis library. Metadata gets stored in a dictionary and image data is made available as a numpy array.
So far everything I've seen has focused on reconstructed volumes. There aren't reconstruction algorithms included in Avizo, only image processing and modeling tools. I suppose, one might use Avizo to filter or modify projection data prior to reconstruction, but the data would need to be exported, then reconstructed, then imported again.

@tacaswell : The volumes are not a cube generally, unless cropping has occurred. For reconstructed volumes, X and Y dims are generally equal, but Z is different. Dims are dictated by (a) camera detector size (num pixels) and (b) binning factor.