Reorganize source code

- `scord` daemon now has its own directory in `src/scord`
- `scord-ctl` daemon now has its own directory in `src/scord-ctl`
- library code now lives under the  `lib` directory
- public rpc definitions now live in `src/lib/rpcs/`
- private rpc definitions for each daemon now live in
  `src/scord/rpcs/` and `src/scord-ctl/rpcs/`, respectively
- `config`, `logger`, and `network` code now live under the `common` directory