tests refactoring
Added tooltip in disabled button
Added logic to prevent update listing in cases descripted in issue MNT-96
Added tests
Fixed bugs in rendering flow of Listing related views
Added Listing view tests
Separated retrieve product process in update Lsting view
Fixed listings tests and views to new delete policy
Changed logic to update a listing
Added new tests to test new update listing logic
Fixed update listing view, moving controller logic in is_valid form function
Fixed form logic in cheking cleaned_data
Fixed listing view due new validation logic in listing form
Fixed logic to show detail listing view
Added tests for listing detail view when it is missing the listingset