PO Line Item Improvements (#340)

* Refactor thumbnail image

* Add paginated list of purchase order line items

* Refactor getBody() function

- No longer "have" to specify
- Can use getTiles for a simpler interface

* Add detail widget for polineitem

* add pricing info

* Receive line items via action button

* tweak color

* update release notes

* linting fixes

lib/widget/notifications.dart

@@ -54,7 +54,8 @@ class _NotificationState extends RefreshableState<NotificationWidget> {
   /*
    * Display an individual notification message
    */
-  List<Widget> renderNotifications(BuildContext context) {
+  @override
+  List<Widget> getTiles(BuildContext context) {
 
     List<Widget> tiles = [];
 
@@ -87,17 +88,4 @@ class _NotificationState extends RefreshableState<NotificationWidget> {
     return tiles;
 
   }
-
-  @override
-  Widget getBody(BuildContext context) {
-    return Center(
-      child: ListView(
-        children: ListTile.divideTiles(
-          context: context,
-          tiles: renderNotifications(context),
-        ).toList()
-      )
-    );
-  }
-
-}
+}