Resolve some todos in server/model:
* Move persistent queue into its own package
* Create Types: StatusValue, SCMKind, RepoVisibly
* Rename struct Repo fields: SCMKind, IsSCMPrivate
- move cli files from `cli/drone` to `cli/`
- move cli main to `cmd/cli/main.go` to match agent and server
- use version from `version/version.go` to match agent and server