Description:
Add an air conditioner mode to the heat_control component. The same concept and operation used for plug in heaters applies equally well to in-wall or window AC units except the logic is reversed.

Related issue (if applicable): fixes #

Pull request in home-assistant.io with documentation (if applicable): home-assistant/home-assistant.io#723

Example entry for configuration.yaml (if applicable):

thermostat:
  platform: heat_control
  name: Study
  heater: switch.study_heater
  target_sensor: sensor.study_temperature
  min_temp: 15
  max_temp: 21
  target_temp: 15
  ac_mode: True

Checklist:

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

• Documentation added/updated in home-assistant.io

If code communicates with devices, web services, or a:

• 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.

This commit adds a new option to the heat_control component, ac_mode.
When set to true, this treats the toggle device as a cooler instead
of a heater. The concept being if you have a window or in-wall ac
unit that doesn't have a built-in thermostat having the home assistant
implemented thermostat would be as useful as for space heaters.