Introducing InitiatingFlow annotation which has to be annotated by initiating flows.

This removes the need for the shareParentSessions parameter of FlowLogic.subFlow. It also has the flow's version number so FlowVersion is now no longer needed.

docs/source/example-code/src/main/kotlin/net/corda/docs/FxTransactionBuildTutorial.kt

@@ -11,6 +11,7 @@ import net.corda.core.crypto.Party
 import net.corda.core.crypto.SecureHash
 import net.corda.core.crypto.sign
 import net.corda.core.flows.FlowLogic
+import net.corda.core.flows.InitiatingFlow
 import net.corda.core.node.PluginServiceHub
 import net.corda.core.node.ServiceHub
 import net.corda.core.node.services.unconsumedStates
@@ -104,6 +105,7 @@ private fun prepareOurInputsAndOutputs(serviceHub: ServiceHub, request: FxReques
 
 // A flow representing creating a transaction that
 // carries out exchange of cash assets.
+@InitiatingFlow
 class ForeignExchangeFlow(val tradeId: String,
                           val baseCurrencyAmount: Amount<Issued<Currency>>,
                           val quoteCurrencyAmount: Amount<Issued<Currency>>,

docs/source/example-code/src/main/kotlin/net/corda/docs/WorkflowTransactionBuildTutorial.kt

@@ -4,6 +4,7 @@ import co.paralleluniverse.fibers.Suspendable
 import net.corda.core.contracts.*
 import net.corda.core.crypto.*
 import net.corda.core.flows.FlowLogic
+import net.corda.core.flows.InitiatingFlow
 import net.corda.core.node.PluginServiceHub
 import net.corda.core.node.ServiceHub
 import net.corda.core.node.services.linearHeadsOfType
@@ -144,6 +145,7 @@ class SubmitTradeApprovalFlow(val tradeId: String,
  * Simple flow to complete a proposal submitted by another party and ensure both nodes
  * end up with a fully signed copy of the state either as APPROVED, or REJECTED
  */
+@InitiatingFlow
 class SubmitCompletionFlow(val ref: StateRef, val verdict: WorkflowState) : FlowLogic<StateAndRef<TradeApprovalContract.State>>() {
     init {
         require(verdict in setOf(WorkflowState.APPROVED, WorkflowState.REJECTED)) {