Simple IKEA lampshade adapter plates

Over the years we have bought IKEA lampshades and, apart from one instance, we have always forgotten to buy the adapter plates for UK light fittings! I have [created adapters in the past](https://www.thingiverse.com/thing:5273024) but I have come to realise that I was over-complicating things. Also, my first SCAD creation was designed to handle the lampshades with just 2 bars, but then we bought a couple of shades with 3 bars...

So I rewrote the SCAD file to reduce the complexity - this one is VERY simple - and thus increase the chance of a successful end product.

Note that this adapter will work with both lamp standards/bases and pendant fittings; in other words, it will work either way up.