Clean up the Create Project UI experiment

Summary

In conclusion of the experiment, we have decided to proceed with the new UI for Project Creation. We need to clean up the experiment, remove the old code and make the new solution permanent.

Todo

• Conclude the experiment
• Remove the new_create_project_ui flag
• Remove obsolete code (old views)
• Update the docs per this comment
• Remove DOMContentLoaded from app/assets/javascripts/pages/projects/new/index.js
• Clean up the use of data-qa-selector in spec/features/*
• Organize code to be in permanent location (currently in an "experiment" folder)
• Move SVGs to gitlab-svg repo
• Change min-width: 215px to width: 215px to ensure SVGs don't get giant
• Add bottom margin on .md sized screens