Add support for setting cover target position and tilt

[manuelkasper]

This adds two new feature flags to Cover:

• SetPositionFeature
  • In addition to the device reporting its current position, if this feature is enabled, then Home Assistant can also set a target position (0-100, onSetPositionCommand) instead of only sending up/down/stop commands.
  • Must be used together with PositionFeature.
• TiltFeature
  • For covers that can also tilt (independently of setting the position). Enables reporting the current tilt level to Home Assistant, and setting a target tilt level (0-100, onTiltCommand) from Home Assistant.

See also #47

The various feature combinations look as follows in the UI:

No features

PositionFeature

SetPositionFeature (+ PositionFeature)

TiltFeature

All features