Allow platform xml namespaces to be used with xml attributes in Alloy

Would be great to allow using xml namespaces to filter attributes based on platform.

For example:

 <Label ios:text="Hello iOS!" android:text="Hello Android!" />

This is a probably over-simplistic example but the only way to do this right now is to have two separate elements:

<Label text="Hello iOS!" platform="ios" />

and

<Label text="Hello Android!" platform="android" />

This can cause problems with some tags/elements where it thinks you have duplicate tags and throws a compile time error.