QMLEngine Way Too Sticky

QML Engine currently has no working way to dump loaded QML and replace it with fresh QML.

A sample project and screen shot have been attached to demonstrate that a given QML Engine does not respond to clearComponentCache().

While only tested on OSX, I have seen it on android.

The goal is to be able to unload the QML from QmlEngine and replace it with another screen. The demo shows 2 windows, a yellow window that is loaded first, then we attempt to remove its QML, then load a second red window for display.

The screen shot clearly shows

In the code pattern the Project Wizard creates, it produces a single QmlEngine on the stack, so Qt has some strategy for handling when lots of QML is loaded.

There is no evidence or code patterns of allocating the QmlEngine on the heap and then deleting that object when we want to change the screens.