Change BottomTabs visibility to Invisible instead of Gone

This change is introduced so BottomTabs are actually rendered when created
This commit also fixes back button issue where it wasn't properly added when pushing screens.

lib/android/app/src/main/java/com/reactnativenavigation/parse/BackButton.java

@@ -58,4 +58,9 @@ public class BackButton extends Button {
         if (!enabled.hasValue()) enabled = defaultOptions.enabled;
         if (!testId.hasValue()) testId = defaultOptions.testId;
     }
+
+    public void setVisible() {
+        visible = new Bool(true);
+        hasValue = true;
+    }
 }

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/bottomtabs/BottomTabsController.java

@@ -155,7 +155,7 @@ public class BottomTabsController extends ParentController implements AHBottomNa
     private void attachTabs() {
         for (int i = (tabs.size() - 1); i >= 0; i--) {
             ViewGroup tab = tabs.get(i).getView();
-            if (i != 0) tab.setVisibility(View.GONE);
+            if (i != 0) tab.setVisibility(View.INVISIBLE);
             getView().addView(tab);
         }
     }
@@ -172,7 +172,7 @@ public class BottomTabsController extends ParentController implements AHBottomNa
 
     @Override
     public void selectTab(final int newIndex) {
-        getCurrentView().setVisibility(View.GONE);
+        getCurrentView().setVisibility(View.INVISIBLE);
         bottomTabs.setCurrentItem(newIndex, false);
         getCurrentView().setVisibility(View.VISIBLE);
     }

lib/android/app/src/main/java/com/reactnativenavigation/viewcontrollers/stack/BackButtonHelper.java

@@ -1,14 +1,13 @@
 package com.reactnativenavigation.viewcontrollers.stack;
 
 import com.reactnativenavigation.parse.Options;
-import com.reactnativenavigation.parse.params.Bool;
 import com.reactnativenavigation.viewcontrollers.ViewController;
 
 public class BackButtonHelper {
     public void addToChild(StackController stack, ViewController child) {
         if (stack.size() <= 1 || child.options.topBar.buttons.left != null || child.options.topBar.buttons.back.visible.isFalse()) return;
         Options options = new Options();
-        options.topBar.buttons.back.visible = new Bool(true);
+        options.topBar.buttons.back.setVisible();
         child.mergeOptions(options);
     }
 }

lib/android/app/src/test/java/com/reactnativenavigation/viewcontrollers/BottomTabsControllerTest.java

@@ -116,7 +116,7 @@ public class BottomTabsControllerTest extends BaseTest {
     public void setTabs_firstChildIsVisibleOtherAreGone() {
         uut.onViewAppeared();
         for (int i = 0; i < uut.getChildControllers().size(); i++) {
-            assertThat(uut.getView().getChildAt(i).getVisibility()).isEqualTo(i == 0 ? View.VISIBLE : View.GONE);
+            assertThat(uut.getView().getChildAt(i).getVisibility()).isEqualTo(i == 0 ? View.VISIBLE : View.INVISIBLE);
         }
     }
 
@@ -128,7 +128,7 @@ public class BottomTabsControllerTest extends BaseTest {
         uut.onTabSelected(3, false);
 
         assertThat(uut.getSelectedIndex()).isEqualTo(3);
-        assertThat(((ViewController) ((List) uut.getChildControllers()).get(0)).getView().getVisibility()).isEqualTo(View.GONE);
+        assertThat(((ViewController) ((List) uut.getChildControllers()).get(0)).getView().getVisibility()).isEqualTo(View.INVISIBLE);
         assertThat(((ViewController) ((List) uut.getChildControllers()).get(3)).getView().getVisibility()).isEqualTo(View.VISIBLE);
         verify(eventEmitter, times(1)).emitBottomTabSelected(0, 3);
     }