feat(category): sort categories directly via sort property on category model

Author: JohnL17

Diff for: addon/components/category-nav.hbs

@@ -22,7 +22,7 @@
         />
       {{/each}}
     {{else}}
-      {{#each this.categories.records as |category|}}
+      {{#each (sort-by "sort" this.categories.records) as |category|}}
         <CategoryNav::Category
           @category={{category}}
           @selected={{@selected}}

Diff for: addon/models/category.js

@@ -7,6 +7,7 @@ export default class CategoryModel extends LocalizedModel {
   @attr color;
   @attr metainfo;
   @attr allowedMimeTypes;
+  @attr sort;
 
   @belongsTo("category", { inverse: "children", async: true }) parent;
   @hasMany("category", { inverse: "parent", async: true }) children;