Dismiss all modals in correct order

When more then one modal was displayed, and dismissAllModals
was called, the top most modal was dismissed until no modals
were visible. This resulted in quirky animation since user saw
all modals getting dismissed.
This commit simply changes to order in which modals are dismissed to
avoid this bug.

android/app/src/main/java/com/reactnativenavigation/controllers/ModalController.java

     }
 
     public void dismissAllModals() {
-        while (isShowing()) {
-            dismissTopModal();
+        for (Modal modal : stack) {
+            modal.dismiss();
         }
+        stack.clear();
     }
 
     public boolean isShowing() {