Low-level claims deletion & maintenance

[marfox]

This PR refines the script for low-level claims deletion (which aims at fixing the bot's errors, usually raised by community feedback on https://www.wikidata.org/wiki/User_talk:Hjfocs) :

• sleep 9 seconds between each deletion
• log in using a credentials JSON file passed as a CLI arg
• log out at the end of work

In addition:

• bump the pywikibot version due to https://phabricator.wikimedia.org/T291202
• set isort multi-line behavior to hanging grid grouped, see https://pycqa.github.io/isort/docs/configuration/multi_line_output_modes.html#5-hanging-grid-grouped
• set isort line length to 88
• switch to the pre-commit CI status badge