Workaround occasional window show bug in Qt 5.0.2

This avoids the problem where the Window is displayed with a
frame but without content.

More details at https://bugs.launchpad.net/bugs/1179716
Add main2.qml to qmlscene example.
Add upstream references to the qmlscene examples.
Add delegate model view example.
When QML calls Go methods convert type if possible
Be gentle to the CPU by avoiding QTBUG-14956

The idle hook is in fact a machine gun rather than firing just
when the application becomes idle. Workaround the issue by
starting/stopping it as necessary.

More details about the Qt behavior at:

https://bugreports.qt-project.org/browse/QTBUG-14956
qml.Object is now an interface.
Window is now based on CommonObject.
Context is now based on CommonObject.
Move C++ fatal errors into Go space
CommonObject => Common