server: Add TransactionId model

server/app/com/xsn/explorer/models/TransactionId.scala

@@ -0,0 +1,18 @@
+package com.xsn.explorer.models
+
+class TransactionId private (val string: String) extends AnyVal
+
+object TransactionId {
+
+  private val pattern = "^[a-f0-9]{64}$".r.pattern
+
+  def from(string: String): Option[TransactionId] = {
+    val lowercaseString = string.toLowerCase
+
+    if (pattern.matcher(lowercaseString).matches()) {
+      Some(new TransactionId(lowercaseString))
+    } else {
+      None
+    }
+  }
+}