Removed Warning, Notify and Fatal:
* `Warning` => `Error` or `Info`
* `Notify` => `Info`
* `Fatal` was never used.
Note that --log-level=warning is still supported for backwards
compatibility, but it is the same as --log-level=error.
Co-authored-by: Julio López <julio+gh@kasten.io>
* cache: refactored reusable portion of cache into separate package
* repo: plumbed through caching for remote repository clients
* repo: plumb through cache in the unit tests
* cache: ensure we only allow absolute cache paths, fixed cache path resolution for remote repositories
