Implement mkdoxy documentation for Aircraftt Design repository

This commit partially addresses the issue Integrate mkdoxy in pipeline.
Creates mkdoxy documentation for files inside Aircraft Design repository.
This also link generated documentation to the UNICADO website.
Following files are editted:
1. .gitlab-ci.yml : clone aircraft-design and libraries repo
2. scripts/copy_aircraft_design_to_docs.py ( Copy aircraft-design to
   docs folder of gitlabio repo.
3. overrides/main.html :Adapted to disply footer logo on all pages
4.  mkdocs.yml : Changed link to documentation.

Issue: #21