Provide ability to force branching to stop at a particular node in level.criteria

[alforj]

Allow user to indicate that they want to stop the branching from a particular node in the level criteria even if the count is not zero (which is stopped via show.empty.child = TRUE). This would allow the tree to stay balanced (from a count perspective) but not force the tree to continue to be drawn out from nodes that don't matter. (e.g., show nodes for each status but only expand out the tree for one of the statuses).