Debugger: Export Debugger::DebuggerItem to fix BlackBerry setup

Task-number: QTCREATORBUG-10189
Change-Id: Icddd09a1a931371133a1d03ca8cf600e76295eac
Reviewed-by: David Kaspar <dkaspar@blackberry.com>
Reviewed-by: hjk <hjk121@nokiamail.com>