This changes `state_information` to return the names and values of
all defined features.
It was originally a "temporary" hack to show some extra, device-specific
information in the cli tool, but now that we have device-defined
features we can leverage them.
This adds a generic interface for all device classes to introspect available device features,
that is necessary to make it easier to support a wide variety of supported devices with different set of features.
This will allow constructing generic interfaces (e.g., in homeassistant) that fetch and change these features without hard-coding the API calls.
`Device.features()` now returns a mapping of `<identifier, Feature>` where the `Feature` contains all necessary information (like the name, the icon, a way to get and change the setting) to present and change the defined feature through its interface.
