Improved security via digital certificates and a PKI

[ahzf]

• Add Open Charging Cloud root certificate
• Make sure, that the versions.json is digitally signed by one or more organizations
• Verify the certificates/signatures of the entire versions.json
• Verify the certificates/signatures of a version
• Verify the certificates/signatures of a version package
• Verify the certificates/signatures of a energy meter public key
• Verify the certificates/signatures of another certificates/signature (build a chain/web of trust)
• Sign entire CTRs