Add dependency list to report

What does this MR do?

Add the dependency list in the Dependency Scanning report using the dependency_files key introduced in common!35 (merged)

• update scanner/parser and its modules to return the packager of a dependency file
• update scanner to propagate the package to the source
• update convert sub-package to extract the dependency files
• refactor the main and convert in order to share the same code b/w gemnasium-python, gemnasium-maven and this very analyzer

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/10071

Does this MR meet the acceptance criteria?

• Changelog entry added
• [-] Documentation created/updated for GitLab EE, if necessary
• [-] Documentation created/updated for this project, if necessary
• [-] Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• [-] Job definition updated, if necessary
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer