Added AJAX based context menu on the project issue list that provide shortcuts for editing, re-assigning, changing the status or the priority, moving or deleting an issue.
The context menu shows up when right-clicking an issue (Opera users have to use Ctrl + left-click instead since right-click can't be reassigned for this browser).
Works with Firefox 2, IE 7 (not perfect), Opera 9 and Safari 2. IE 6 doesn't display submenus.

git-svn-id: http://redmine.rubyforge.org/svn/trunk@872 e93f8b46-1217-0410-a6f0-8f06a7374b81