Add new setAlertParent function (#207)

Author: zachicecreamcohn

src/components/alert.ts

@@ -4,10 +4,18 @@
 // =============================================================================
 
 
-import {$body, $N, CustomElementView, register} from '../';
+import {$body, $N, CustomElementView, register, HTMLView} from '../';
 
 let $openAlert: Alert|undefined;
-const $alertParent = $N('div', {class: 'snackbar'}, $body);
+let $alertParent = $N('div', {class: 'snackbar'}, $body);
+
+/**
+ * Sets the container element where new alerts will be appended.
+ * @param parent - The HTMLView element to use as the alert container
+ */
+export function setAlertParent(parent: HTMLView) {
+  $alertParent = parent;
+}
 
 
 @register('x-alert')