The LegendTemplate widget currently contains code to control layer visibility,
there is no way to turn this off.  The impact is that if the legend template
does not contain the appropriate layer visibility checkboxes, or it is used in
conjunction with a popup widget that does change layer visibility, then
unexpected things happen to layer visibility (like changes made in popups are lost).

The proposed change is to add an attribute to the legendtemplate widget that
would control whether the widget will attempt to set layer visibility or not. 
Turning this off would fix interaction with other widgets, or with templates
that don't contain layer visibility controls at all.