Remove ctant witness inclusions for Pedersen Comm

[CPerezz]

As mentioned in #38 That's actually a problem since we
define value and bid_value as constant witnesses
(constraint to a constant).
This means that we're harcoding these values in the
ProverKey & VerifierKey and therefore,
the circuit is not reusable.

Solved it by assigning a normal witness inclusion for these
values.

Closes #38

[LukePearson1]

This looks good to me. The prover and verifier key will no longer be concrete.

One thing that could be changed is to import EXTENDED_GENERATOR from JubJub and also define an extended GENERATOR_NUMS in JubJub. This way the from doesn't need to be computed at compile time.

As the suggested changes can both done in JubJub, thus addressed in another issue and PR combo - this PR can be merged.

[CPerezz]

This looks good to me. The prover and verifier key will no longer be concrete.

One thing that could be changed is to import EXTENDED_GENERATOR from JubJub and also define an extended GENERATOR_NUMS in JubJub. This way the from doesn't need to be computed at compile time.

As the suggested changes can both done in JubJub, thus addressed in another issue and PR combo - this PR can be merged.

1. The import of GENERATOR_EXTENDED is a good idea, I'll open a followup issue for it.
2. The Exteneded generators are already exported from jubjub. See: Implements #31 - Generators available as extended jubjub#34