#311 Added domains element definition in memo.xsd

This what I suggested:

```xml
<memo>
  <domains>
    <domain>example.com</domain>
    <domain>example-2.com</domain>
  </domains>
  <ports>
    <port>80</port>
    <port>8080</port>
  </ports>
</memo>
```

This is what we have now, in your branch:

```xml
<memo>
  <domains>
    <domain>example.com</domain>
    <domain>example-2.com</domain>
    <ports>
      <port>80</port>
      <port>8080</port>
    </ports>
  </domains>
</memo>
```

I think that it is semantically not correct. And it's against the spirit of XML. Don't you think?