PoseArray should have "axes" as a display option

[aleeper]

The Pose display plugin has a dropdown to select the shape between "arrow" and "axes".
However, the PoseArray plugin has no such feature., though I think it would be trivial to add. (This is probably purely for historical reasons, as I think the plugin was originally developed to show 2D navigation path planning results only.)

Note that a good PoseArray plugin would more or less solve the use case in #652 as well.