HVAC: Add a model for a zone

```
    <zone id="1">
      <name>ZONE 1</name>
      <enabled>on</enabled>
      <currentActivity>home</currentActivity>
      <rt>76.0</rt>
      <rh>59</rh>
      <fan>low</fan>
      <htsp>70.0</htsp>
      <clsp>76.0</clsp>
      <hold>off</hold>
      <otmr/>
      <zoneconditioning>idle</zoneconditioning>
      <damperposition>15</damperposition>
    </zone>
```