[BREAKING] Updated Capabilities

[s-kostyuk]

After a small review already documented Capabilities was updated. This pull request contains some breaking changes.

• updated documentation for base Thing instances in REST API:
  • "commands" field is provided only in Actuators;
  • "is_active" and "state" field are now provided only if corresponding Capabilities are implemented;
• updated current Capabilities:
  • updated Multi-Mode Capability name, fields and description;
  • switched to floating point values for Has Brightness and Has Color HSB capability fields;
  • renamed Available interface to IsAvailable;
  • switched to IntEnum for Thing States;
• added all Capabilities which were already declared in documentation:
  • Multi-Mode;
  • Has Brightness;
  • Has Color HSB;
  • Has Color RGB;
  • Has Volume;
• AbsActuator interface for now is left unchanged.

Closes #111