This creates the cuspidal subspace of the space of Bianchi modular forms
over the field F (an imaginary quadratic field) on Γ0(N) with weight 2.
The level N should be an ideal in the maximal order of F.
The optional argument VorData may be set equal to VoronoiData(M) where
M is a previously computed space of forms over the same field. This avoids
repeating the time-consuming precomputations that depend only on the field.
