0.5.1

Release v0.5.1

Changelog :

- the login flow will no longer ask for a context name and select
  default if none is provided through `--context`
- Added list operation : `get devices` now prints a list of devices.
  Lists can be filtered with labels. See readme.
- If no changes are made in `drg edit` the result is not send to the
  server
- The `edit` operation now present YAML data for nicer editing
- Bug fixes and small improvements.