This moves all magic-folder configs to a single YAML
file. We load legacy config fine and don't mess with
legacy config unless you use a magic-folder command that
changes the config.
Increase test coverage
Improve error-handling for directories if you ask for JSON from
the /uri endpoint, but an error occurs (you get a proper HTTP
status code and a valid JSON object).
For 'tahoe magic-folder status' e now retrieve *all* the remote data
required in the CLI before doing anything else so that errors can be
shown immediately. Use the improved JSON endpoints to print better
errors.
Adds:
- a JSON endpoint
- CLI to display information
- QueuedItem + IQueuedItem for uploader/downloader
- IProgress interface + PercentProgress implementation
- progress= args to many upload/download APIs
