Handle delete expense case for accounting export summary

What's Changed

• Add pre-commit hook for flake8 by @ashwin1111 in #510
• Bump gevent by @ashwin1111 in #509
• Handle delete expense case for accounting export summary by @ashwin1111 in #505
• Reduce pytest time by @ashwin1111 in #511

Full Changelog: e19ebd7...437d86c