Minor code and repo cleanup

Armin Felder requested to merge kc-metadata-import-cleanup into master
  • Remove unused imports
  • Provide an actually matching requirements.txt
  • Add .gitignore for cache and data files
  • Apply style fixes from Flake8 except where noted in provided .flake8 config
  • Improve Markdown formatting of README.md
  • Use exclude instead of blacklist
  • Configure Metadata URL for analyze.py the same way as for main.py (instead of hard-coding some URL and commenting that one needs to change it)

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