Add SmartThings Cover platform and add cover device classes

[andrewsayre]

Description:

Adds SmartThings Cover platform that represents SmartThings devices that have open/close related capabilities. Highlights:

• Supports open/close for doors, garage doors, and window shades.
• Cover position is supported for device that implement the switchLevel capability.
• Battery level is reported as a state attribute if the battery capability is implemented by the device.
• Cover entities are automatically created if supported by the device.
• Adds 6 new device classes to the Cover platform per Add additional Cover device classes architecture#153 (curtain, door, shade, shutter, blind, and awning)

BREAKING CHANGE: With the addition of the SmartThings Cover platform, the SmartThings Sensor platform will no longer represent Door, Garage Door and Window Share attributes. Additionally, if the cover device reports battery status, the value will be present as a state attribute (battery_level) and not a discrete sensor.

Pull request in home-assistant.io with documentation: home-assistant/home-assistant.io#8625

Pull request in developers.home-assistant with dev documentation: home-assistant/developers.home-assistant#187

Checklist:

• The code change is tested and works locally.
• Local tests pass with tox. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.

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

• Documentation added/updated in home-assistant.io

If the code does not interact with devices:

• Tests have been added to verify that the new code works.

[andrewsayre]

@balloob Can you take a look at this when you get a chance? I think it's ready to move forward.

[MartinHjelmare]

Last comment I think.

[MartinHjelmare]

Nice!