Revert qmlInfo to a streamable type

As it stands qmlinfo is:

1. Difficult to use (which comes first the object or the message?)
2. Difficult to include - Qt's <QmlInfo> convention is not honored
3. Inconsistent with the rest of Qt (which has a convenient streaming version for each debug type).

We can still achieve i18n just as easily with qmlInfo(obj) << tr("Cannot assign type %1").arg(name)