Clean up getmodels.py

[akloster]

I was interested in squiggle-level analysis of nanopore data, and your script didn't work for the limited/old collection of files I had. The second column of the model files would be a "variant", not a mean. I changed the code to use Pandas for reading HDF and writing CSV. You may use header=False in the calls to pd.write_csv if you want to omit the header row.

This version should also be robust to column reordering in future/past fast5 formats.