Added invert flag for position for actuators with inverted position

[ghost]

Description:

Some shutter actuators have an inverted position indication compared to Home assistant. In this case, 100% means "closed" and 0% "open". The invert option allows to

Related issue (if applicable): None

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.github.io#<home-assistant.github.io PR number goes here>

Example entry for configuration.yaml (if applicable):

cover:
  platform: knx
  name: Shutter
  updown_address: 1/140
  stop_address: 1/141
  setposition_address: 1/142
  getposition_address: 1/144
  invert_position: True

Checklist:

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).
• New dependencies are only imported inside functions that use them (example).
• New dependencies have been added to requirements_all.txt by running script/gen_requirements_all.py.
• New files were added to .coveragerc.

If the code does not interact with devices:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass
• Tests have been added to verify that the new code works.