improve error on theme upload, add gif to allowed uploads

app/controllers/admin/themes_controller.rb

@@ -16,7 +16,7 @@ class Admin::ThemesController < Admin::AdminController
       filename = params[:file]&.original_filename || File.basename(path)
       upload = UploadCreator.new(file, filename, for_theme: true).create_for(current_user.id)
       if upload.errors.count > 0
-        render json: upload.errors, status: :unprocessable_entity
+        render_json_error upload
       else
         render json: { upload_id: upload.id }, status: :created
       end

config/site_settings.yml

@@ -714,7 +714,7 @@ files:
     min: 5
     max: 150
   theme_authorized_extensions:
-    default: 'jpg|jpeg|png|woff|woff2|svg|eot|ttf|otf'
+    default: 'jpg|jpeg|png|woff|woff2|svg|eot|ttf|otf|gif'
     type: list
   authorized_extensions:
     client: true