Various cleanups to AMQP and Kryo serialisation:

* PartyAndCertificate serialiser has been converted to deal with just CertPath
* Removed X500Name serialiser as we no longer use the BC implementation and have our own CordaX500Name
* Converted X509 cert serialiser to use Java certs and not BC X509 cert holder
* Added to test to AMQP serialisation to make sure c'tor is invoked on deserialisation

core/src/test/kotlin/net/corda/core/contracts/PrivacySaltTest.kt

@@ -0,0 +1,13 @@
+package net.corda.core.contracts
+
+import org.assertj.core.api.Assertions.assertThatExceptionOfType
+import org.junit.Test
+
+class PrivacySaltTest {
+    @Test
+    fun `all-zero PrivacySalt not allowed`() {
+        assertThatExceptionOfType(IllegalArgumentException::class.java).isThrownBy {
+            PrivacySalt(ByteArray(32))
+        }.withMessage("Privacy salt should not be all zeros.")
+    }
+}