Refactor the repository

This PR brings a heavy repo refactoring. The repo now only contains the principal components of the Custodian and the tools that are needed to set them up.

Here is the list of what has changed:

• Removed old/unnecessary files from the repo
• Moved components from src/core to the top folder
• Removed src/core/common which has been moved to (another repo)[https://gitlab.com/data-custodian/custodian-go]
• Moved the two PoCs (src/poc/mjf and src/poc/epfl-css) to separate repositories - MJF, EPFL-CSS
• Rename sdc-cli into custodian-cli and move it to another repo
• Moved the csscontract.go from the demo/clients/contract_signer_helper in the CSS setup repo
• Moved src/deploy/secrets-generator to the top folder
• Moved src/demo/kms to the top folder
• Removed src/demo
• Removed src/deploy
• Removed src
• Added keycloak to platform
• Updated .gitlab-ci, the Makefile and the README