Lua support for PolyObjects

Hopefully self-explanatory. Unless anyone else really wants to do the work for me, this is just a sort of reminder to myself to add the support in at some point.

I guess this issue can be closed now?

I haven't done anything for PolyObject Lua support yet, so not yet.

mentioned in merge request !1140 (merged)

closed via merge request !1140 (merged)

mentioned in commit bd9fda8c