A miner selects a sector size when pledging

[laser]

Description

A miner should select a sector size when pledging, i.e. when miner create runs. To start with, we should support Test and TwoFiftySixMiB. The choice of sector size should be constrained to some enumeration of values in Go code.

Acceptance criteria

[ ] - update miner create command to require a new sector size-argument
[ ] - rust-fil-proofs uses selected sector size when packing pieces into sectors and sealing
[ ] - go-filecoin actors use selected sector size when verifying seal and PoSt proofs
[ ] - modify gengen setup.json to include miner's sector size
[ ] - make sure that 1KiB sectors are used when in test proofs mode and prevent 1KiB sectors from being used when not in test proofs mode