Turn on GPU support for all children of the layerContainerDiv

This seems to remove all kinds of flicker and jumpiness, and to me it feels
also like it makes panning on slow mobile devices smoother.

theme/default/style.css

@@ -487,6 +487,13 @@ a.olControlZoomOut {
     transition: opacity 0.2s linear;
 }
 
+.olTileImage, .olLayerDiv {
+    -webkit-transform: translate3d(0, 0, 0);
+    -moz-transform: translate3d(0, 0, 0);
+    -o-transform: translate3d(0, 0, 0);
+    transform: translate3d(0, 0, 0);
+}
+
 /* override any max-width image settings (e.g. bootstrap.css) */
 img.olTileImage {
     max-width: none;