Failing functional test for filtered item list
Failing tests for filtering tagged items
Cleaned up imports
Custom QuerySet for items to filter for tags
Cleaned up ItemModelTest
Renamed view classes
Fixed ItemQuerySet.tagged filter
Added tests for tag view
Implemented tags-view

Tags are now linked to the tags view which is
just like the index view, but it filters by tags
Tags on items directly link to the tag view
Updated tests, extracted example tag to constant
Use slugs instead of tag names
Implemented filtering for tags with a new view

This implements the features of pull request #8

Merge branch 'tag-filters'