Allowing multiple signature algorithms (#250)

Basic crypto API to support 5 signature schemes and MetaData-ed signatures.
Supported schemes: (1) RSA_SHA256, (2) ECDSA_SECP256K1_SHA256, (3) ECDSA_SECP256R1_SHA256, (4) EDDSA_ED25519_SHA512, (5) SPHINCS-256_SHA512.

To sign a transaction, a signer should create a MetaData wrapper that contains transaction's merkle root and some extra information, such as signer's public key, timestamp and visibleInputs. Actually, MetaData is utilised to support a practical partial, blind and extra-data attached signature model.
When a MetaData object is signed, the signer sends a TransactionSignature object that contains the signed output and the corresponding MetaData object.

Remarks: 
This is an temporary solution for signature algorithmic agility. Further development is required for a robust and extensible Crypto Manager/Provider PKI that will support certificate creation, key generation, signing/verifying, deterministic key derivation, encoding formats, SGX/HSM support, identity and key management, versioning, revocation, asynchronicity, metadata, partial sig. policies etc.

node/src/main/kotlin/net/corda/node/serialization/DefaultWhitelist.kt

@@ -46,6 +46,7 @@ class DefaultWhitelist : CordaPluginRegistry() {
             addToWhitelist(BigDecimal::class.java)
             addToWhitelist(LocalDate::class.java)
             addToWhitelist(Period::class.java)
+            addToWhitelist(BitSet::class.java)
         }
         return true
     }