[ETCM-313] and [ETCM-316]: Header skeleton using new branch resolver

src/main/scala/io/iohk/ethereum/blockchain/sync/fast/FastSyncBranchResolver.scala

@@ -0,0 +1,18 @@
+package io.iohk.ethereum.blockchain.sync.fast
+
+import akka.actor.Actor
+import io.iohk.ethereum.network.Peer
+
+class FastSyncBranchResolver extends Actor {
+
+  override def receive: Receive = ???
+
+}
+
+object FastSyncBranchResolver {
+  sealed trait BranchResolverRequest
+  case object StartBranchResolver extends BranchResolverRequest
+
+  sealed trait BranchResolverResponse
+  case class BranchResolvedSuccessful(firstCommonBlockNumber: BigInt, masterPeer: Peer) extends BranchResolverResponse
+}