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/attachment_widget.dart

@@ -147,19 +147,7 @@ class _AttachmentWidgetState extends RefreshableState<AttachmentWidget> {
   }
 
   @override
-  Widget getBody(BuildContext context) {
-    return Center(
-        child: ListView(
-          children: ListTile.divideTiles(
-              context: context,
-              tiles: attachmentTiles(context)
-          ).toList(),
-        )
-    );
-  }
-
-
-  List<Widget> attachmentTiles(BuildContext context) {
+  List<Widget> getTiles(BuildContext context) {
 
     List<Widget> tiles = [];