Navigation stack native primitives (#139)

Adds support for stack navigation primitives (UINavigationViewController and Android fragment container with back button support)

android/src/main/java/com/swmansion/rnscreens/ScreenStackViewManager.java

@@ -0,0 +1,62 @@
+package com.swmansion.rnscreens;
+
+import android.view.View;
+import android.view.ViewGroup;
+
+import com.facebook.react.module.annotations.ReactModule;
+import com.facebook.react.uimanager.ThemedReactContext;
+import com.facebook.react.uimanager.ViewGroupManager;
+
+@ReactModule(name = ScreenStackViewManager.REACT_CLASS)
+public class ScreenStackViewManager extends ViewGroupManager<ScreenStack> {
+
+  protected static final String REACT_CLASS = "RNSScreenStack";
+
+  @Override
+  public String getName() {
+    return REACT_CLASS;
+  }
+
+  @Override
+  protected ScreenStack createViewInstance(ThemedReactContext reactContext) {
+    return new ScreenStack(reactContext);
+  }
+
+  @Override
+  public void addView(ScreenStack parent, View child, int index) {
+    if (!(child instanceof Screen)) {
+      throw new IllegalArgumentException("Attempt attach child that is not of type RNScreen");
+    }
+    parent.addScreen((Screen) child, index);
+  }
+
+  @Override
+  public void removeViewAt(ScreenStack parent, int index) {
+    prepareOutTransition(parent.getScreenAt(index));
+    parent.removeScreenAt(index);
+  }
+
+  private void prepareOutTransition(Screen screen) {
+    startTransitionRecursive(screen);
+  }
+
+  private void startTransitionRecursive(ViewGroup parent) {
+    for (int i = 0, size = parent.getChildCount(); i < size; i++) {
+      View child = parent.getChildAt(i);
+      parent.startViewTransition(child);
+      if (child instanceof ViewGroup) {
+        startTransitionRecursive((ViewGroup) child);
+      }
+    }
+  }
+
+  @Override
+  public int getChildCount(ScreenStack parent) {
+    return parent.getScreenCount();
+  }
+
+  @Override
+  public View getChildAt(ScreenStack parent, int index) {
+    return parent.getScreenAt(index);
+  }
+}