'reversed' connections in outerwall model

There is an inconsistency: in internalWall port_a of layMul is connected to propsBus_a. However in outerWall port_b is connected to propsBus_b. This is counterintuitive. Also I have made a component which is a combination of these two models and then I can not specify a building structure that works in both modes because the material layers are reversed. This pull request solves my issue but means that all your construction layers will need to be reversed. Therefor I understand if you rather not pull this, still I think it is the right thing to do! =)