fix(android): cleanup build.gradle & fix #218 (#238)

This changes the following:
 - Fixes #218 
 - Removed unused Fabric Maven config
 - Versions now correctly checking `rootProject.ext.X` instead of `rootProject.X` to match behaviour from all other libs (RNFB needs changing as well 🙈)
 - Swapped `implementation` for `api` for react native sources - only used to build.


![image](https://user-images.githubusercontent.com/5347038/50959941-1af23980-14bc-11e9-8677-e60f3ee744e7.png)
![image](https://user-images.githubusercontent.com/5347038/50959955-22b1de00-14bc-11e9-8afa-d1abbba46a64.png)

cc @terrytianliang

android/build.gradle

@@ -3,12 +3,10 @@ buildscript {
   repositories {
     google()
     jcenter()
-        maven {
-            url 'https://maven.fabric.io/public'
-        }
   }
   dependencies {
     classpath 'com.android.tools.build:gradle:3.2.1'
+    //noinspection DifferentKotlinGradleVersion
     classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
   }
 }
@@ -16,17 +14,20 @@ buildscript {
 apply plugin: 'com.android.library'
 apply plugin: 'kotlin-android'
 
-
+def DEFAULT_TARGET_SDK_VERSION = 27
 def DEFAULT_COMPILE_SDK_VERSION = 27
 def DEFAULT_BUILD_TOOLS_VERSION = "28.0.3"
-def DEFAULT_TARGET_SDK_VERSION = 27
+
+def getExtOrDefault(name, defaultValue) {
+  return rootProject.ext.has(name) ? rootProject.ext.get(name) : defaultValue
+}
 
 android {
-    compileSdkVersion rootProject.hasProperty('compileSdkVersion') ? rootProject.compileSdkVersion : DEFAULT_COMPILE_SDK_VERSION
-    buildToolsVersion rootProject.hasProperty('buildToolsVersion') ? rootProject.buildToolsVersion : DEFAULT_BUILD_TOOLS_VERSION
+  compileSdkVersion getExtOrDefault('compileSdkVersion', DEFAULT_COMPILE_SDK_VERSION)
+  buildToolsVersion getExtOrDefault('buildToolsVersion', DEFAULT_BUILD_TOOLS_VERSION)
   defaultConfig {
     minSdkVersion 16
-        targetSdkVersion rootProject.hasProperty('targetSdkVersion') ? rootProject.targetSdkVersion : DEFAULT_TARGET_SDK_VERSION
+    targetSdkVersion getExtOrDefault('targetSdkVersion', DEFAULT_TARGET_SDK_VERSION)
     versionCode 1
     versionName "1.0"
   }
@@ -35,8 +36,6 @@ android {
       minifyEnabled false
     }
   }
-    productFlavors {
-    }
   lintOptions {
     disable 'GradleCompatible'
   }
@@ -49,44 +48,75 @@ android {
 repositories {
   mavenCentral()
   jcenter()
-    maven {
-        url 'https://maven.google.com/'
-        name 'Google'
+
+  def found = false
+  def defaultDir = null
+  def androidSourcesName = 'React Native sources'
+
+  if (rootProject.ext.has('reactNativeAndroidRoot')) {
+    defaultDir = rootProject.ext.get('reactNativeAndroidRoot')
+  } else {
+    defaultDir = new File(
+      projectDir,
+      '/../../../node_modules/react-native/android'
+    )
   }
 
-    // Stolen from react-native-firebase, thanks dudes!
-    def found = false
-    def parentDir = rootProject.projectDir
-    def reactNativeAndroidName = 'React Native (Node Modules)'
+  if (defaultDir.exists()) {
+    maven {
+      url defaultDir.toString()
+      name androidSourcesName
+    }
 
-    1.upto(4, {
+    logger.quiet(":${project.name}:reactNativeAndroidRoot ${defaultDir.canonicalPath}")
+    found = true
+  } else {
+    def parentDir = rootProject.projectDir
+
+    1.upto(5, {
       if (found) return true
       parentDir = parentDir.parentFile
-        def reactNativeAndroid = new File(
+
+      def androidSourcesDir = new File(
+        parentDir,
+        'node_modules/react-native'
+      )
+
+      def androidPrebuiltBinaryDir = new File(
         parentDir,
         'node_modules/react-native/android'
       )
 
-        if (reactNativeAndroid.exists()) {
+      if (androidPrebuiltBinaryDir.exists()) {
         maven {
-                url reactNativeAndroid.toString()
-                name reactNativeAndroidName
+          url androidPrebuiltBinaryDir.toString()
+          name androidSourcesName
         }
 
-            println "${project.name}: using React Native sources from ${reactNativeAndroid.toString()}"
+        logger.quiet(":${project.name}:reactNativeAndroidRoot ${androidPrebuiltBinaryDir.canonicalPath}")
+        found = true
+      } else if (androidSourcesDir.exists()) {
+        maven {
+          url androidSourcesDir.toString()
+          name androidSourcesName
+        }
+
+        logger.quiet(":${project.name}:reactNativeAndroidRoot ${androidSourcesDir.canonicalPath}")
         found = true
       }
     })
+  }
 
   if (!found) {
     throw new GradleException(
-                "${project.name}: unable to locate React Native Android sources, " +
-                        "ensure you have you installed React Native as a dependency and try again."
+      "${project.name}: unable to locate React Native android sources. " +
+        "Ensure you have you installed React Native as a dependency in your project and try again."
     )
   }
 }
 
 dependencies {
-    implementation 'com.facebook.react:react-native:+'
+  //noinspection GradleDynamicVersion
+  api 'com.facebook.react:react-native:+'
   implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
 }