Use double resolution logo to support hires displays

IPython/html/static/notebook/js/kernelselector.js

@@ -85,7 +85,7 b' define(['
         this.events.on('spec_changed.Kernel', function(event, data) {
             that.current_selection = data.name;
             that.element.find("#current_kernel_spec").find('.kernel_name').text(data.display_name);
-            that.element.find("#current_kernel_logo").attr("src", "/kernelspecs/"+data.name+"/logo-32.png");
+            that.element.find("#current_kernel_logo").attr("src", "/kernelspecs/"+data.name+"/logo-64.png");
         });
         
         this.events.on('kernel_created.Session', function(event, data) {

IPython/html/static/notebook/less/kernelselector.less

@@ -9,4 +9,9 b''
             margin-top:0px;
         }
     }
+    
+    & > img#current_kernel_logo {
+        width: 32px;
+        height: 32px;
+    }
 }

IPython/html/static/style/style.min.css

@@ -9680,6 +9680,10 b' fieldset[disabled] #kernel_selector_widget > button.active {'
 #kernel_selector_widget > button > span.caret {
   margin-top: 0px;
 }
+#kernel_selector_widget > img#current_kernel_logo {
+  width: 32px;
+  height: 32px;
+}
 #menubar {
   margin-top: 0px;
   box-sizing: border-box;