Take account of body tolerances in Converter_ACDC_DCDC

This extends the StandardBox to have a customisable fab (i.e. nominal body line) to silkscreen offset. It already has the courtyard offset. Then drive these both from the script, and add a YAML key to set it.

Update the Muarata NCS1 module to use the right tolerance from the datasheet.

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While this may seem wasteful of board space, it's the only way to be 100% sure the component will not violate courtyard clearances in real life. In practice, most converters are so large relative to the tolerances that the tolerances won't matter much, and users can choose to be more aggressive with packing if they wish to "risk it".

Left, original; right, new:

In this case, the NCS1 module has a (0.70, 0.65) body tolerance. The fab layer is drawn at the mid point using the maximum material condition (21.87, 8.2), so we see there's (0.35, 0.325) extra clearance.