Layers manager: add in popup menu option to hide all coppers layers but active layer.

Design rules: increase number of vias and tracks sizes
Pcbnew: netlist reader: change from my recent commits to keep netnames in pads for footprints not in netlist
(allow an user to place some footprints by hand, set pads netnames and do not lost these netnames when loading a netlsit)
Fix other very minor issues.

common/drawframe.cpp

@@ -823,6 +823,9 @@ void EDA_DRAW_FRAME::UpdateStatusBar()
     // We already decided the formatter above
     Line.Printf( locformatter, dXpos, dYpos );
     SetStatusText( Line, 3 );
+
+    // refresh units display
+    DisplayUnitsMsg();
 }