ProjectsController#add_issue moved to IssuesController#new.

Tracker can now be changed/selected on the new issue form. This action can be invoked without the tracker_id parameter (the first enabled tracker will be used by default).

git-svn-id: http://redmine.rubyforge.org/svn/trunk@1080 e93f8b46-1217-0410-a6f0-8f06a7374b81