changed material layer order back so that the order is consistent for all components: layMul.port_b is connected to propsBus_a
Also added this to the documentation of the structure package.
added section in top package containing list of important changes to library since before annex60
Merge pull request #102 from open-ideas/issue86_outerWall

Changed material layers the other way around compared to issue 86, non-backward implication is the order change for internal walls !