Fixed exomiser-html-description image and markdown locations

[Shettland]

PR checklist

• exomiser-html-description was bugged probably due to .svg format, so I changed the image to .png format. Also the markdown locations in services.json for irma, exomeeb and trios was not correct, so I fixed it.
• 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.
• CHANGELOG.md is updated.
• 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