Added support for colored KNX lights

[Julius2342]

Description:

Added support for colored KNX lights

Example entry for configuration.yaml (if applicable):

light:
  - platform: knx
    name: Kitchen
    address: '1/0/9'
    color_address: '1/0/11'

Checklist:

• [x ] The code change is tested and works locally.

If user exposed functionality or configuration variables are added/changed:

• Documentation added/updated in home-assistant.github.io

If the code communicates with devices, web services, or third-party tools:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• New dependencies have been added to the REQUIREMENTS variable ([example][ex-requir]).
• New dependencies are only imported inside functions that use them ([example][ex-import]).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.