implement toggling of online/offline storage/retrieval deals

[laser]

Makes incremental progress towards #1920.

What's in this PR?

This PR allows storage miners to toggle consideration (auto-rejection) of storage and retrieval deals based on whether the deals expect the data to be transferred on or offline. Note that there doesn't yet exist a concept of offline retrieval deals, so that particular configuration option is a noop.

Usage

From the miner side

12:45 $ lotus-storage-miner retrieval-deals selection list
consider online retrieval deals: true
consider offline retrieval deals: true
✔ ~/dev
12:45 $ lotus-storage-miner retrieval-deals selection reject --online
✔ ~/dev
12:45 $ lotus-storage-miner retrieval-deals selection list
consider online retrieval deals: false
consider offline retrieval deals: true
✔ ~/dev
12:45 $ lotus-storage-miner retrieval-deals selection reset
✔ ~/dev
12:45 $ lotus-storage-miner retrieval-deals selection list
consider online retrieval deals: true
consider offline retrieval deals: true
12:45 $ lotus-storage-miner retrieval-deals selection reject --online
✔ ~/dev

From the client side

✔ ~/dev
12:45 $ lotus client retrieve bafkreic4vyeyy4u7jilvv7iq2s6blhxfzmlo44lxbdgozyknpwph4u33ri /var/folders/8h/gmmbhq1s5tb8sk9011sy2wkw0000gn/T/localnet.XXXX.FcH62cM6/retrieved-data.txt
2020-06-26T12:46:13.856-0700    WARN    main    lotus/main.go:81        Retrieval Failed:
    github.com/filecoin-project/lotus/cli.glob..func19
        /var/folders/8h/gmmbhq1s5tb8sk9011sy2wkw0000gn/T/localnet.XXXX.FcH62cM6/build/cli/client.go:473
  - RetrieveUnixfs: Retrieval Proposal Rejected: deal rejected: miner is not accepting online retrieval deals