Add elevation to dict

[fabaff]

Description:
Add elevation to the output of the /api/config endpoint.

$ curl -X GET -H "x-ha-access: YOUR_PASSWORD" -H "Content-Type: application/json" http://localhost:8123/api/config
{
    "components": [
        "recorder",
        "http",
        "weather.openweathermap",
        "api",
        "websocket_api",
        "frontend",
        "sensor.time_date",
        "sun",
        "device_tracker",
        "group",
        "automation"
    ],
    "config_dir": "/home/ha/.homeassistant",
    "elevation": 590,
    "latitude": 45.92,
    "location_name": "Home",
    "longitude": 6.52,
    "time_zone": "Europe/Zurich",
    "unit_system": {
        "length": "km",
        "mass": "g",
        "temperature": "\\u00b0C",
        "volume": "L"
    },
    "version": "0.37.0.dev0"
}

Related issue (if applicable): fixes #5441

Pull request in home-assistant.github.io with documentation (if applicable): home-assistant/home-assistant.io#1830

Example entry for configuration.yaml (if applicable):

homeassistant:
  latitude: 45.92
  longitude: 6.52
  elevation: 590
  unit_system: metric
  # Time zone is CET/CEST+1
  time_zone: Europe/Zurich
  name: Home

Checklist:

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

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

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.

[balloob]

You're sometimes switching quotes from single to double, and sometimes from double to single. What's going on ?

[fabaff]

For Logger messages and some other natural language messages in a lot of cases we are using double quotes and no periods at the end. Constants are usually just wrapped with single quotes. As far as I remember doesn't PEP say something about this but when ever I came across a file I will update it to match the majority of your files to keep the style synced.

Here I was a bit too eager to align the usage of the quotes that I touched the exceptions.

[balloob]

The change to the dict itself is fine. I'm not sure about the quote changing as it's not migrating to a consistent quote.