Customisable Latching Broom Holder w/ additional options

Thanks to Greg for an amazing OpenSCAD design. My skill level isn't close to Greg's but I've added a few things I needed and figured I'd share :-

- Option to counterbore instead of countersink (for pan head screws)
- Customisable mount depth - hopefully I've calculated this correctly, it should be the offset from the broom to the wall, enabling storing things that need to be further from the wall than the default (if you enter a value less than the default, it will be ignored.)
- Made enabling the first layer inset optional and disabled by default. I love this feature, but it slows down compile considerably - Customizer will now work with it disabled; there may just be a little clean-up to do afterwards.