Update todo_item_controller.rb

Changes:
* removed duplicated before_filter
* removed ||= association, as @issue is a new issue, .tracker is always nil at this time.
* direct assignment of project on issue creation
* direct assignment of tracker on issue creation
* throw error_no_tracker_in_project earlier, if there is no available tracker
* remove @todo_item.issue.delete() as you have delete dependation (model: :dependent => :delete)
* minor codecleanup (identation, init_journal)