Added command to determine resolution of Hi-C experiment

[fgroll]

This command will help determining the map resolution, as described by Rao et al., 2014, i.e. the smallest bin size at which 80% of bins have at least 1000 contacts. The output is a simple table of file name, bin size and percentage of bins passing the threshold. Additionally, a plot can be created:

Since I couldn't find an existing module to fit the function in, and the limitation for multiprocessing functions to only accept functions defined at the top-level, _resolution_bins_passing_threshold is defined directly within the fanc_commands.py module.