Even out the Gerbveiw zoom steps and increase the max.

Fixes: lp:1773215
* https://bugs.launchpad.net/kicad/+bug/1773215

gerbview/gbr_screen.cpp

@@ -51,21 +51,23 @@ static const double gbrZoomList[] =
     ZOOM_FACTOR( 0.15 ),
     ZOOM_FACTOR( 0.2 ),
     ZOOM_FACTOR( 0.3 ),
-    ZOOM_FACTOR( 0.45 ),
-    ZOOM_FACTOR( 0.7 ),
+    ZOOM_FACTOR( 0.44 ),
+    ZOOM_FACTOR( 0.66 ),
     ZOOM_FACTOR( 1.0 ),
     ZOOM_FACTOR( 1.5 ),
     ZOOM_FACTOR( 2.2 ),
     ZOOM_FACTOR( 3.5 ),
     ZOOM_FACTOR( 5.0 ),
     ZOOM_FACTOR( 8.0 ),
-    ZOOM_FACTOR( 11.0 ),
-    ZOOM_FACTOR( 15.0 ),
+    ZOOM_FACTOR( 13.0 ),
     ZOOM_FACTOR( 20.0 ),
     ZOOM_FACTOR( 35.0 ),
     ZOOM_FACTOR( 50.0 ),
-    ZOOM_FACTOR( 100.0 ),
-    ZOOM_FACTOR( 200.0 )
+    ZOOM_FACTOR( 80.0 ),
+    ZOOM_FACTOR( 130.0 ),
+    ZOOM_FACTOR( 200.0 ),
+    ZOOM_FACTOR( 350.0 ),
+    ZOOM_FACTOR( 500.0 )
 };