Don't render full category information in part API

- Lots of data duplication!
- Just send the category ID (and the category name)
-

InvenTree/part/templates/part/category.html

@@ -151,11 +151,11 @@
             },
             {
                 sortable: true,
-                field: 'category',
+                field: 'category_name',
                 title: 'Category',
                 formatter: function(value, row, index, field) {
                     if (row.category) {
-                        return renderLink(row.category.pathstring, row.category.url);
+                        return renderLink(row.category_name, "/part/category/" + row.category + "/");
                     }
                     else {
                         return '';

InvenTree/part/templates/part/subcategories.html

@@ -4,7 +4,7 @@
  <div class="panel panel-default">
    <div class="panel-heading">
      <h4 class="panel-title">
-       <a data-toggle="collapse" href="#collapse1">Child Categories</a><span class='badge'>{{ children|length }}</span>
+       <a data-toggle="collapse" href="#collapse1">{{ children | length }} Child Categories</a>
      </h4>
    </div>
    <div id="collapse1" class="panel-collapse collapse">