Proxy refactoring

[mkrzyzanowski]

Motivation and Context

Proxy is poorly documented and codebase related to its handling requires some love. This PR is about addressing this issue.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• [x] I have read the CONTRIBUTING document.
• [x] My code follows the code styleguide of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have added tests to cover my changes.