Reorganize native dep download and extraction (#154)

Summary:
This moves the native setup to a separate gradle file and unpacks everything outside the build folder. That way we don't throw everything away on every incremental build.

This is an intermediate step to get to a more declarative setup like Fresco has it and get rid of the individual hacks we have for every download.
Pull Request resolved: https://github.com/facebook/Sonar/pull/154

Reviewed By: jknoxville

Differential Revision: D8833812

Pulled By: passy

fbshipit-source-id: 2424c9d6e22e6092c04af344e06939b4a6aba041

android/sample/build.gradle

@@ -7,7 +7,7 @@ android {
     defaultConfig {
         minSdkVersion rootProject.minSdkVersion
         testInstrumentationRunner 'android.support.test.runner.AndroidJUnitRunner'
-        applicationId "com.facebook.sonar.sample"
+        applicationId 'com.facebook.sonar.sample'
     }
 
     lintOptions {