Add status to repo

When a repo is created, it is either fully formed (`--no-content` or `--url`) or requires asynchronous work to be usable. In the latter case, this status is currently tracked in a command, which is an unnecessary layer of indirection.

Better than linking the repo to its create-repo command in order to determine the download/extract status, the repo itself should hold the status so that installation can act on this state.

Use Case

• A user creates a repo using `iso-url`.
• While the ISO file is downloading, the user views the `razor repos` collection.
• The `razor repos` collection contains no information on its status, even though it is not ready yet.

In Scope

• Add `create_command` field to repo.
• Link respective `create-repo` command to repo.
• Update `create-repo` command to say that the repo will be downloaded asynchronously when it will (`iso-url` supplied)
• Add `repo.create_command.status` to repo view in view.rb.
• Update command status values to the more descriptive `pending`, `downloading`, `extracting`, `finished`, `error-retry`, and `failed` statuses (currently `pending`, `running`, `finished`, `failed`).
• Update command status when created, download starts, extract starts, and extract/move finishes.
• Use status `transient-error` if there is an error which will be retried (e.g. 404).
• Use status `errored` when the error is fatal/retried for the last time.
• Client: Show the repo's status in `razor repos` via views.yaml.

Optional

• Include the progress of the download (percent complete?)