added message to LnZapEvent and interface

app/src/main/java/com/vitorpamplona/amethyst/service/model/LnZapEvent.kt

@@ -36,6 +36,10 @@ class LnZapEvent(
             null
         }
     }
+    override fun message(): String {
+        return message
+    }
+    val message = content
 
     override fun containedPost(): Event? = try {
         description()?.let {

app/src/main/java/com/vitorpamplona/amethyst/service/model/LnZapEventInterface.kt

@@ -13,4 +13,6 @@ interface LnZapEventInterface : EventInterface {
     fun amount(): BigDecimal?
 
     fun containedPost(): Event?
+
+    fun message(): String
 }