Add Gradle build files.

templates/android/template/build.gradle

@@ -1,4 +1,26 @@
-ant.importBuild 'build.xml'
+// Top-level build file where you can add configuration options common to all sub-projects/modules.
+
+buildscript {
+    repositories {
+        jcenter()
+    }
+    dependencies {
+        classpath 'com.android.tools.build:gradle:2.1.0'
+
+        // NOTE: Do not place your application dependencies here; they belong
+        // in the individual module build.gradle files
+    }
+}
+
+allprojects {
+    repositories {
+        jcenter()
+    }
+}
+
+task clean(type: Delete) {
+    delete rootProject.buildDir
+}
 
 task wrapper(type: Wrapper) {
     gradleVersion = '::ANDROID_GRADLE_VERSION::'