Consume Android artifacts from npm

Summary:
This lets us say goodbye to Maven Central. This will greatly simplify
and speed up the release process as releasing Android artifacts to
Maven Central adds a lot of [complexity](https://github.com/facebook/react-native/blob/master/Releases-publish.md)
and delays the whole release by several hours when we have to wait
for the artifacts to propagate.

This diff assumes there's a local Maven repo at
`node_modules/react-native/android`.

The second part once this lands is to change our `release.sh` script to
output the artifacts under `react-native/android` before publishing to
npm.

This adds 3.7MB to the size of `node_modules` of any app. However,
we just download eagerly what we'd normally download later via Gradle.

**Test plan**

Released RN including a local Maven repo into Sinopia:

    $ cd react-native
    # Updated version in gradle.properties to 0.21.0
    $ ./gradlew ReactAndroid:installArchives
    # Moved everything in .m2/repository/com/facebook/react to react-native/android
    $ ls react-native/android
    com/facebook/react/react-native/0.21.0/react-native-0.21.0.aar
    com/facebook/react/react-native/0.21.0/react-native-0.21.0.pom
    com/facebook/react/react-native/maven-metadata.xml
    ...

    # Set version in package.json to 0.21.0
    $ npm set registry http://localhost:4873/
    $ npm publish

Created and ran an app:

   $ cd /tmp
   $ react-native init AndroidNpm
   $ cd AndroidNpm
   $ react-native run-android

It worked.

Checked that we're using the artifacts from node_modules/react-native/android:

    $ cd android
    $ ./gradlew app:dependencies
    compile - Classpath for compiling the main sources.
    +--- com.android.support:appcompat-v7:23.0.1
    |    \--- com.android.support:support-v4:23.0.1
    |         \--- com.android.support:support-annotations:23.0.1
    \--- com.facebook.react:react-native:+ -> 0.21.0
         +--- com.google.code.findbugs:jsr305:3.0.0
         +--- com.facebook.stetho:stetho-okhttp:1.2.0
    ...

Checked that Android Studio can find the source jars (you can navigate to RN sources in Android Studio). Opened the new project as described in the [docs](https://facebook.github.io/react-native/docs/android-setup.html#editing-your-app-s-java-code-in-android-studio).

public

Reviewed By: bestander

Differential Revision: D2912557

fb-gh-sync-id: 251c180518a3fb9bb8e80963b236e982d65533be
shipit-source-id: 251c180518a3fb9bb8e80963b236e982d65533be

local-cli/generator-android/templates/src/app/build.gradle

@@ -62,8 +62,7 @@ import com.android.build.OutputFile
 apply from: "react.gradle"
 
 /**
- * Set this to true to create three separate APKs instead of one:
+ * Set this to true to create two separate APKs instead of one:
- *   - A universal APK that works on all devices
  *   - An APK that only works on ARM devices
  *   - An APK that only works on x86 devices
  * The advantage is the size of the APK is reduced by about 4MB.
@@ -93,9 +92,9 @@ android {
     }
     splits {
         abi {
-            enable enableSeparateBuildPerCPUArchitecture
-            universalApk false
             reset()
+            enable enableSeparateBuildPerCPUArchitecture
+            universalApk false  // If true, also generate a universal APK
             include "armeabi-v7a", "x86"
         }
     }
@@ -123,5 +122,5 @@ android {
 dependencies {
     compile fileTree(dir: "libs", include: ["*.jar"])
     compile "com.android.support:appcompat-v7:23.0.1"
-    compile "com.facebook.react:react-native:0.13.0"
+    compile "com.facebook.react:react-native:+"  // From node_modules
 }

local-cli/generator-android/templates/src/build.gradle

@@ -16,5 +16,9 @@ allprojects {
     repositories {
         mavenLocal()
         jcenter()
+        maven {
+            // All of React Native (JS, Obj-C sources, Android binaries) is installed from npm
+            url "$projectDir/../../node_modules/react-native/android"
+        }
     }
 }

package.json

@@ -82,7 +82,7 @@
   "files": [
     "React",
     "React.podspec",
-    "ReactAndroid",
+    "android",
     "Libraries",
     "packager",
     "cli.js",