Ohm (Omega) Added to Basic Electronics Stencil

I added an ohm symbol to the basic electronics stencil. I had found another stencil that also had the common unit symbols (A W V <ohm>) and thought it would be nice to add those, and then realized that really only Ohm was hard to consistently draw freehand. Also there wasn't space to add anything else at the same scale. The placement gives it just enough room that its walls don't intersect with anything else and is roughly centered so that being close to the connector doesn't introduce too much structural weakness.