[UX] Nematic functional has an attribute `pitch`, but corresponds to 2*Pi/pitch

[joshichaitanya3]

From Amine Missaoui:

"I wanted to calculate the director field for a simple case of an achiral 5CB. So I set the pitch to a large value (about 200 because the "lnem.pitch = inf" command does not work)."

The pitch attribute for the Nematic functional is confusing for the user, since it actually means 2*Pi / pitch (= q).

Don't know whether we want to keep pitch or introduce the q, or keep both.

[softmattertheory]

We can rename this to wavevector. @joshichaitanya3 or @ConduitDan please make the change and amend the examples (if any!)

[ConduitDan]

I'll take this on in my upcoming round of fixes

[ConduitDan]

revisiting this