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.
This is going to throw a pretty confusing error when the file fails to open.  Probably an `AttributeError`  about `md_dict` not having the `x_pixel_size` parameter.  Maybe init `md_dict` to be `None` before you try to open the file and see if it is still `None` afterwards?  I'm saying this with little context of what is actually in these NetCDF files, so take this with a grain of salt...