Get_key_management finalized

[Mathixx]

Key management part of the Identity-server specs implemented

@twake/crypto module completed with :

• key generator (supporting ed25519 et curve25519 algorithms)
• fonctions for converting JSON object in canonical JSON then signing them (following matrix.org specs)

matrix-identity-server/src/db/index.ts completed with createKeypair and deleteKey methods

For each new module, corresponding tests have been created