Keep non-LP connections to layer nodes when moving a layer

[joshuaKnauber]

When moving a layer the connections to other nodes should be kept.. Right now all nodes are disconnected from the layer and then reconnected once the layer is moved. LP should keep track of the previous connections and try to connect them again.

Without putting too much thought into it, it should probably connect them not to the same layer, but the layer with the same index. This could be wrong though.
The main use case would probably be moving a layer from the bottom that has other things connected as the base. Now that it's not the bottom most layer anymore, the connected nodes should still be the base, so it should be connected to what's not the bottom most layer.