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/part_suppliers.dart

@@ -51,11 +51,7 @@ class _PartSupplierState extends RefreshableState<PartSupplierWidget> {
     InvenTreeSupplierPart _part = _supplierParts[index];
 
     return ListTile(
-      leading: InvenTreeAPI().getImage(
-        _part.supplierImage,
-        width: 40,
-        height: 40,
-      ),
+      leading: InvenTreeAPI().getThumbnail(_part.supplierImage),
       title: Text("${_part.SKU}"),
       subtitle: Text("${_part.manufacturerName}: ${_part.MPN}"),
       onTap: () async {