Add error message when type registration fails outside of QML module loading

Add error message when type registration namespace is not set.

If one does
qmlRegisterUncreatableType<EnumTest>("enumtest",1,0,"enumtest", "empty");
and tries to access console.log("enumtest.high:" + enumtest.high); we only print out ReferenceError.

It would be more clear to give programmer indication why the enumtest was not registered, e.g. give indication that it should be uppercase.