Setup the React Gradle Plugin

Author: cortinico

Diff for: android/app/build.gradle

@@ -1,4 +1,5 @@
 apply plugin: "com.android.application"
+apply plugin: "com.facebook.react"
 
 import com.android.build.OutputFile
 
@@ -83,6 +84,11 @@ project.ext.react = [
 
 apply from: "../../node_modules/react-native/react.gradle"
 
+react {
+    reactRoot = rootProject.file("../node_modules/react-native/")
+    codegenDir = rootProject.file("../node_modules/react-native-codegen/")
+}
+
 /**
  * Set this to true to create two separate APKs instead of one:
  *   - An APK that only works on ARM devices