protobuf: add signal_queue_entry and use it in thread_core_entry and task_core_entry

Add signal_queue_entry signals_s for shared signals to task_core_entry
and signals_p for private signals to thread_core_entry.

Signed-off-by: Ruslan Kuprieiev <kupruser@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>