Debugger: Implement "Create Full Backtrace" for LLDB

Task-number: QTCREATORBUG-11642
Change-Id: I92d7cde1e5021ab06ad72a00645184c41dae0e6b
Reviewed-by: Ulf Hermann <ulf.hermann@digia.com>
Reviewed-by: hjk <hjk121@nokiamail.com>