Enhanced the Issue Bulk Copy feature:

* Add a Copy option to the Context menu for multiple issues.
* Added assigned to, status, start and due date options to the move/copy form.
* Allow Issue#move_to to change attributes on the moved/copied issue.

  #4117

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3122 e93f8b46-1217-0410-a6f0-8f06a7374b81