Deprecated FlowLogic.getCounterpartyMarker as it's complicated and probably not used (replacement is to use sub-flows).

Also made flow registration require the client flow class rather than any old class.

samples/trader-demo/src/main/kotlin/net/corda/traderdemo/flow/BuyerFlow.kt

@@ -31,7 +31,7 @@ class BuyerFlow(val otherParty: Party,
                 it.automaticallyExtractAttachments = true
                 it.storePath
             }
-            services.registerFlowInitiator(SellerFlow::class.java) { BuyerFlow(it, attachmentsPath.toString()) }
+            services.registerServiceFlow(SellerFlow::class.java) { BuyerFlow(it, attachmentsPath.toString()) }
         }
     }