add init to Account & Transaction

Sources/Blockchain/Models/Transaction.swift

@@ -12,4 +12,11 @@ class Transaction {
     var receiver: String
     var amount: Int
     var type: String
+    
+    init(sender: String, receiver: String, amount: Int, type: String) {
+        self.sender = sender
+        self.receiver = receiver
+        self.amount = amount
+        self.type = type
+    }
 }