Adds an assertion on issues deletion when deleting a project (#5381).
Fixed: private subprojects names may be revealed on issue summary report (#5360).
Refactor: move method to helper.
Refactor: extract error to new method with before_filter.
Refactor: Extract duplicated code to a new method.
Refactor: Split IssuesController#new to #new and #create to match REST pattern.
Refactor: Move the rest of the routing tests to RoutingTest.
Move more routing tests into the routing integration test.
Adding missing setter for Query#available_columns
Refactor: Move method to Query model
