Prohibit adding duplicate Items

Probably a redirect to the edit view would be better?
Add test case test_unable_to_add_duplicate
Use ExistingUserTest.create_example_item() instead of duplicated code
Tags are saved as a list in the search index
Add new tags to duplicate
Merge branch 'Prohibit-duplicate' of https://github.com/enkore/pypo into enkore-Prohibit-duplicate
New tags from adding a duplicate are searchable
Merge pull request #5 from enkore/Prohibit-duplicate

Prohibit adding duplicate Items and instead adding
all tags of the duplicate to the original
Fixed error in from refactoring functional tests
Added facets for tags in the search

Changed the haystack requirement to a fork of haystack
with a fix for faceting with Whoosh until it is implemented
in the main line
Facets are shown in the search
Facets are shown on the list page
item_single: display tags directly in extra line, give timespace more space
Changed markup requires changing the tests slightly
Merge pull request #6 from enkore/item-tag

Item tag display
Merge branch 'master' into tag-facets

Conflicts:
	functional_tests/tests.py
JS handler to toggle offcanavas rows
Cleaned up tests, removed duplication
Navbar block is now called navbar instead of sidebar
Show tags in a sidebar