Disable binding optimizer when debugging QML apps

Setting QML_DISABLE_OPTIMIZER=1 in the environment of the application prevents QDeclarativeEngine to optimize simple bindings. This should enable us to set breakpoints also on simple bindings, e.g.

Example

Text {
  property string name: "Unknown"
  text: name
}

A breakpoint on "text: name" is hit as soon as name is changed if QML_DISABLE_OPTIMIZER is set, otherwise the binding is optimized & not executed by JavaScript.