refactoring
add edit item page

* add edit action
* add edit view
* up item model
* add page header to the HelperPage
up UsedItem model
up phpbbModel

* update order for related items
add partial view for back button
up item create view
show msg on item page if an item has been updated
up create item view

* set a new order for form fields
up UsedItem model

* add filter for title and description
up item view page

* make new lines for description visible (better readability)
up UsedItem model

* remove limit for description length
up MarketPlace controller

* small refactoring
up/add tests

* tests for ItemEdit page
* test for front page (before and after login)
* tests for DeleteItem page
* tests for Items page (items for active user)
* add new data to fixtures. Update previous tests.