Solder mask integrity testing.

ADDED DRC test for solder mask aperture bridging copper from different
nets.
ADDED visualization of minimum web width processing for solder masks.
ADDED allow_soldermask_bridges property for footprints.

Fixes https://gitlab.com/kicad/code/kicad/issues/2183

Fixes https://gitlab.com/kicad/code/kicad/issues/1792

common/view/view.cpp

@@ -1567,6 +1567,14 @@ bool VIEW::IsVisible( const VIEW_ITEM* aItem ) const
 }
 
 
+bool VIEW::HasItem( const VIEW_ITEM* aItem ) const
+{
+    const VIEW_ITEM_DATA* viewData = aItem->viewPrivData();
+
+    return viewData && viewData->m_view == this;
+}
+
+
 void VIEW::Update( const VIEW_ITEM* aItem ) const
 {
     Update( aItem, ALL );