[Code quality] Rename bins to bin_edges in tools.hist_utilities

[kreczko]

The correct naming should be bin_edges instead of bins in order to make the code more comprehensive. Affected functions in tools.hist_utilities are

• https://github.com/BristolTopGroup/DailyPythonScripts/blob/master/tools/hist_utilities.py#L134
• https://github.com/BristolTopGroup/DailyPythonScripts/blob/master/tools/hist_utilities.py#L29