client: Add javafx utilities and basic WalletMonitor models

client/src/main/kotlin/com/r3corda/client/fxutils/EventStreamFold.kt

@@ -0,0 +1,38 @@
+package com.r3corda.client.fxutils
+
+import javafx.application.Platform
+import javafx.beans.property.SimpleObjectProperty
+import javafx.beans.value.ObservableValue
+import javafx.collections.FXCollections
+import javafx.collections.ObservableList
+import org.reactfx.EventStream
+
+/**
+ * Simple utilities for converting an [EventStream] into an [ObservableValue]/[ObservableList]
+ */
+
+fun <A, B> EventStream<A>.foldToObservable(initial: B, folderFun: (A, B) -> B): ObservableValue<B> {
+    val result = SimpleObjectProperty<B>(initial)
+    subscribe {
+        Platform.runLater {
+            result.set(folderFun(it, result.get()))
+        }
+    }
+    return result
+}
+
+fun <A, B, C> EventStream<A>.foldToObservableList(
+        initialAccumulator: C, folderFun: (A, C, ObservableList<B>) -> C
+): ObservableList<B> {
+    val result = FXCollections.observableArrayList<B>()
+    /**
+     * This capture is fine, as [Platform.runLater] runs closures in order
+     */
+    var currentAccumulator = initialAccumulator
+    subscribe {
+        Platform.runLater {
+            currentAccumulator = folderFun(it, currentAccumulator, result)
+        }
+    }
+    return result
+}