[ALOY-1487] Support using dashes and other special characters in XML element IDs

I'd like to be able to use dashes (and other special characters) in IDs for XML elements:

<Alloy>
  <Label id="my-label" />
</Alloy>

Which currently compiles to this syntax error:

    $.__views.my - label = Ti.UI.createLabel({
        id: "my-label"
    });

Which should become:

    $.__views["my-label"] = Ti.UI.createLabel({
        id: "my-label"
    });

Notes: * Generated code for adding child views, event listeners and so on should also use the bracket notation for these type of IDs. * Probably it's best to always use this notation and let Uglify optimise where possible. * Special characters in classes already work fine.