Refactored almost everything

There are some major fundemental changes with the library. For instance, now we will be treating the `Wellness::System` similar to how we treat `Rack`.

```ruby
  system = Wellness::System.new('some_system')
  system.use(Wellness::Services::RedisService, { ... })
  system.use(Wellness::Services::PostgresService, { ... })

  config.middleware.insert_before(
    '::ActiveRecord::QueryCache',
    'Wellness::Middleware',
    system
  )
```

The `Wellness::Services::Base` hasn't changed too much, `#check` is still working just find, `#passed_check` is deprecated, `#failed_check` is deprecated. Currently they will just `#warn` when it is used.