Integrate One Attestation API

[mbrandenburger]

The attestation module in FPC is currently highly dependable on PDO crypto. To better focus on a useful attestation library that may be uses in various projects, the one-attestation-api project will provide a generic attestation library.

The idea is to integrate the one-attestation-api into FPC. This would enable DCAP based attestation as mentioned #771.

Related open issues:

• Generalize attestation support #15
• Attestation mechanism: SGX DCAP #175