Allow W3C-compliant IDs as an IRI.

Fixes blackberry/BB10-Webworks-Packager#134

This approach allows widgets to have IRI-formatted id attributes
which comply with section 7.6.1 of "Packaged Web Apps (Widgets) -
Packaging and XML Configuration (Second Edition)". These attributes
will now be sanely normalized into the reverse-dotted notation
common across the various BlackBerry SDKs.