Add file viewer branding options

svelte/src/util/SuccessMessage.svelte

@@ -0,0 +1,18 @@
+<script>
+let s = false
+let m = ""
+
+export const set = (success, message) => {
+	s = success
+	m = message
+}
+export const clear = () => {
+	m = ""
+}
+</script>
+
+{#if m}
+	<div class:highlight_green={s} class:highlight_red={!s}>
+		{m}
+	</div>
+{/if}