[feature request] Add waiting icon when paraview is busy

When Paraview is processing a long task, we have no indication for when it has done. It could be a good thing to have a visual information about when it is processing, for example a cursor icon change (a loading weel or a tiny hourglass).

It seems possible in Qt with QApplication::setOverrideCursor(Qt::WaitCursor) and QApplication::restoreOverrideCursor() when it's done.

I think it could make the paraview experience more comfortable, and it will avoid some misclicking when paraview is busy.

What do you think about it?