Zebra should follow OS directory conventions better

[teor2345]

Is your feature request related to a problem? Please describe.

Zebra doesn't follow the config convention for any platform.

Zebra doesn't follow the cache convention for macOS and Windows.

Describe the solution you'd like

• use directories-next to find application-specific paths
  • https://docs.rs/directories-next/2.0.0/directories_next/struct.ProjectDirs.html#method.cache_dir
• use ProjectDirs::cache_dir for caches
• use ProjectDirs::config_dir for configs
• update any deployment scripts that provide custom configs
• update the acceptance tests?
• update the relevant documentation

This is a breaking change for config and cache locations.

Describe alternatives you've considered

We could just not do this, and most people wouldn't notice. But some OSes (and automated tools) might do bad things with Zebra's configs or cache.

[teor2345]

This isn't a priority for Zebra right now.