Make image preview scalable

src/main/kotlin/moe/nea/firmament/util/propertyutil.kt

@@ -0,0 +1,7 @@
+package moe.nea.firmament.util
+
+import kotlin.properties.ReadOnlyProperty
+
+fun <T, V, M> ReadOnlyProperty<T, V>.map(mapper: (V) -> M): ReadOnlyProperty<T, M> {
+    return ReadOnlyProperty { thisRef, property -> mapper(this@map.getValue(thisRef, property)) }
+}