Only disable scrollbars on Android and iOS

Previously scrollbars were disabled on all touch devices. This meant
that they were disabled on Windows when touch was detected. Windows does
in fact have useful scrollbars even in touch mode. Fixes Issue #1172

core/util/browser.js

@@ -64,6 +64,10 @@ export function isIOS() {
             !!(/ipod/i).exec(navigator.platform));
 }
 
+export function isAndroid() {
+    return navigator && !!(/android/i).exec(navigator.userAgent);
+}
+
 export function isSafari() {
     return navigator && (navigator.userAgent.indexOf('Safari') !== -1 &&
                          navigator.userAgent.indexOf('Chrome') === -1);