Widget preview refresh

It is possible to stop the automatic visualization refresh of widget when configuring them.
It could be useful if the datasource has huge amount of data and rendering the widget is long (i.e. a Chart with hundreds thousand point in it)

To disable the auto refresh, the Refresh preview on property change must bu unchecked.

The refresh button in the to bar will show if the widget has pending change :

	No pending change
	Pendng change

By clicking on the Refresh button, the widget will be updated.