[QML PFD]: Fixes an issue by which the PFD was continuing to process
events even when it was no longer visible. This specifically sets the
processed states to 0 as long as the PFD is not visible, and sets them to
the corresponding UAVO when they are.

On OSX with Qt 4.8, this saved 14% processor load.
Merge pull request #918 from kubark42/fix-qml-cpu-usage

Fixes an issue by which the PFD was continuing to process events even when it was no longer visible.