Add a way to skip parameters in categories

[randrej]

Using your config, let's look at Operational Amplifiers. They're a subgroup of Amplifiers, which is a subgroup of Integrated Circuits. Since Amplifiers specify Supply Current, whenever you're importing an opamp (say, a TL072), you'll be asked for Supply Current which is not really something listed in opamp datasheets.

It'd be nice if there was an _omit_parameters field to ignore these things.