up CategoryController

* add delete action
up Category model

* add afterDelete hook. it disables items related to category
up script.js

* confirm delete category
up

* show only items with active categories
up category view page

* show delete button
* show success/error messages
add functional tests for CategoryDeletePage
up CategoryTest

* add delete method
up CategoryFixture

* make it depends on UsedItemFixture
up test for CategoryPage

* ensure category has 2 buttons: ‘update’ and ‘delete’
up Sandbox