Sloth-ci

- Switch from Travis CI to GitHub Actions.

- Change the convention for naming extension and validator modules to `sloth_ci_ext_name` and `sloth_ci_val_name` respectively.
- Update code for the latest Python and Cliar.
- Update dependencies.
- Switch from Sphinx to Foliant.

- Bed, API: Bed: Code refactored to allow extending app listener.

- Server config: Auth section can now contain multiple login:password pairs.

- CLI: Fixed a critical issue with not working CLI if API auth was provided.

- API: Trigger: When invoking `trigger` directly via web API with `wait=1`, you can now define the `success_url` and `fail_url` params to be redirected to after the build completes or fails.
- API: Auth is now optional.