Stock display (#379)

* Display stock quantity more prominently

* Cleanup search widget

* Update for stock_detail widget

* More tweaks

* Change bottom bar icon

* Display boolean parameters appropriately

* Adds ability to edit part parameters

* Bump icon size a bit

* Improvements to filter options

- Allow filtering by "option" type
- To start with, filter stock by status code

* Remove debug message

* Remove getTriState method

- No longer needed
- Remove associated unit tests

* Adjust filters based on server API version

* Muted colors

lib/api.dart

@@ -1332,7 +1332,20 @@ class InvenTreeAPI {
 
   static String get staticThumb => "/static/img/blank_image.thumbnail.png";
 
-  CachedNetworkImage getThumbnail(String imageUrl, {double size = 40}) => getImage(imageUrl, width: size, height: size);
+  CachedNetworkImage? getThumbnail(String imageUrl, {double size = 40, bool hideIfNull = false}) {
+
+    if (hideIfNull) {
+      if (imageUrl.isEmpty) {
+        return null;
+      }
+    }
+
+    return getImage(
+        imageUrl,
+        width: size,
+        height: size
+    );
+  }
 
   /*
    * Load image from the InvenTree server,