KMC better area configured

[kevinjoshai]

What

1. Override configured property for Area element.

Why

1. All areas respond to SD request, regardless of being configured in the Elk project, so the default configured property for Element base class is insufficient for Areas. It is more correct to see if the Area is referenced by a Zone or Keypad. This is what Elk's own sample code does. This will allow Home Assistant users with the auto configuration setting to only see Alarm Control Panels for the Areas they have in their Elk project.

Fixes #75