Show back button by default on screen push

src/deprecated/platformSpecificDeprecated.android.js

 function navigatorPush(navigator, params) {
   addNavigatorParams(params, navigator);
   addNavigatorButtons(params);
+  addTitleBarBackButtonIfNeeded(params);
   addNavigationStyleParams(params);
 
   params.screenId = params.screen;
   }
 }
 
+function addTitleBarBackButtonIfNeeded(screen) {
+  const leftButton = getLeftButton(screen);
+  if (!leftButton) {
+    screen.leftButton = {
+      id: 'back'
+    }
+  }
+}
+
 function getLeftButton(screen) {
   if (screen.navigatorButtons && screen.navigatorButtons.leftButton) {
     return screen.navigatorButtons.leftButton;