Prevent bumping a thread when it's stickied

This prevents all stickied threads from having their own bump order. We
want stickies to all stay in the same order.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

board/models.py

@@ -204,6 +204,7 @@ def post_created(sender, instance, created, **kwargs):
                 instance.bump
                 and instance.op.bump
                 and instance.op.replies.count() < instance.board.autosink
+                and not instance.op.sticky
             ):
                 instance.op.last_bump = timezone.now()
                 instance.op.save()