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/company_list.dart

@@ -69,14 +69,10 @@ class _CompanyListState extends PaginatedSearchState<PaginatedCompanyList> {
     return ListTile(
       title: Text(company.name),
       subtitle: Text(company.description),
-      leading: InvenTreeAPI().getImage(
-        company.image,
-        width: 40,
-        height: 40
-      ),
+      leading: InvenTreeAPI().getThumbnail(company.image),
       onTap: () async {
         Navigator.push(context, MaterialPageRoute(builder: (context) => CompanyDetailWidget(company)));
       },
     );
   }
-}
+}