[ALOY-202] Implement a "nolayout" attribute (or something similar) in tags

There will be times when we want to create an element in markup, but don't want to include it in the view hierarchy. A simple example might be a nav button in a navigation group. I want to be able to create the button in markup so I don't have to create it from scratch in code, or create a whole separate controller triad for it. The format could work something like this:

index.xml

<Alloy>
    <Window>
        <NavigationGroup>
            <Window title="Window 1" id="win1">
                <Label>Window 1</Label>
                <Button id="rightNavButton" nolayout="true"/>
            </Window>
        </NavigationGroup>
    </Window>
</Alloy>

index.js

$.win1.rightNavButton = $.rightNavButton;
$.index.open();