Separate Halo2 parameter and circuit synthesis

[lopeetall]

For the Taiga team:
anoma/taiga#157 (comment)

When using the Halo2 backend the structure should be made the same as with Plonk, where a setup command generates a chosen number of parameters and serializes them to a file, and the prove and verify commands can read parameters from a file. This will solve the Taiga team's problem and make the Vamp-IR subcommand structure more unified.