Removed ad hoc path for wkhtmlpdf and better catching error

[saramonzon]

• Closes #275
• Closes #243

PR checklist

• [x] This comment contains a description of changes (with reason).
• [x] Make sure your code lints (black and flake8).
• If a new tamplate was added make sure:
  • [ ] Template's schema is added in templates/services.json.
  • [ ] Template's pipeline's documentation in assets/reports/md/template.md is added.
  • [ ] Results Documentation in assets/reports/results/template.md is updated.
• [x] CHANGELOG.md is updated.
• [x] README.md is updated (including new tool citations and authors/contributors).
• [ ] If you know a new user was added to the SFTP, make sure you added it to templates/sftp_user.json