I3utils

Hi Sebastian,

This is my commit for the script that generates the `<weighted_aeff>.hdf5` file used in the `aeff` and `reco` stages. The help for this script should be fairly self-explanatory, and the only inputs required are the three hdf5 files for nue, numu, and nutau (same as used in the PaPA analysis parameterization steps). These original <flavor>.hdf5 files are generated from the raw simulated data in `.i3` file format, and the needed keys are saved. Let me know what you'd like me to modify, if anything.

Best,
Tim