More wooden support pieces as official scenery additions

[ZeeMaji]

The set of wooden support scenery pieces that ship with the game is pretty incomplete, i think it would be a very nice and desireable addition to have a half height support structure piece, a support structure wall piece, and a half height version of that wall piece. Possibly more but the three i mentioned should be pretty easy to make.

[ZeeMaji]

As of #294 the pieces mentioned in this issue have been implemented. but i'll leave this open as there are other wooden support pieces that could be added in the future. Such as the diagonal pieces brought up in that PR.