Integration

This merge introduces a modified .gitlab-ci.yml containing 3 build stages:

• connect-southbound: to check the southbound api communication with the controller.
• connect-northbound: to check the northbound communication with the controller.
• build-vo-sdn: Builds the project vo-sdn.

Also introduces a new file flows_headless.json that is a modified version of flows.json but without the ui nodes. This file is essential to make this project run over Eclipse runners.

Upon approval, these changes will be merged with the main branch.