Sync projection mode between operator and customized qt widget

Use the ProjectionEnabled variable on the paraview server as a means of synchronizing the projection mode between prop edit operator and customized qtItem widget, since the operator cannot easily get isChecked() status from the pqPropertyWidget.

Note: even if the Projection is not required to initiate the ProportionalEditSphere in the .sbt file, it is still required to be placed in the <View> for synchronizing the projection direction later when projection mode is ON.

The items variable under pqSMTKItemWidget is the pointer of a vector consisting of mixed types of ValueItems. Is there a way of reducing the repeated usage of std::static_pointer_cast<smtk::attribute::DoubleItem/IntItem>?

@aron.helser I can rebase on you operator with the preview function if you want to merge that first.