System variables and Windows nightly installer change

[craftyjon]

@eelik

However, there’s still a problem with the 3D libraries : in old designs the footprints embedded into the board file refer to the old library path. You may need to add the old KISYS3DMOD variable and point it to the wanted 3D library folder. (I think this is why the original blog post announcement was taken down for a while. Let’s see what kind of instructions they’ll give us later.)

We’re trying to implement some way of fixing this automatically (in most cases) so that we don’t need to ask people to follow special instructions.