Optimize user setting page for mobile browser (#1924)

* Remove overflow because it blocks scrolling on mobile safari.

* Add “-webkit-overflow-scrolling: touch;” to enable smooth scroll on mobile safari and other webkit browsers.

* Use radio buttons in user setting page.

Because select tags with long text are not fit in the width of mobile devices.

* Add flex property to fit labels to devise width.

* Change font size of select.

It causes auto zooming on mobile safari.

app/assets/stylesheets/admin.scss

@@ -120,10 +120,12 @@
   @media screen and (max-width: 600px) {
     display: block;
     overflow-y: auto;
+    -webkit-overflow-scrolling: touch;
 
     .sidebar-wrapper, .content-wrapper {
       flex: 0 0 auto;
       height: auto;
+      overflow: initial;
     }
 
     .sidebar {