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/third-party/overrides/RSocket/build.gradle

@@ -0,0 +1,31 @@
+apply plugin: 'com.android.library'
+
+android {
+    compileSdkVersion rootProject.compileSdkVersion
+    buildToolsVersion rootProject.buildToolsVersion
+
+    defaultConfig {
+        minSdkVersion rootProject.minSdkVersion
+        targetSdkVersion rootProject.targetSdkVersion
+        externalNativeBuild {
+            cmake {
+                arguments '-DANDROID_TOOLCHAIN=clang'
+            }
+        }
+    }
+    lintOptions {
+        abortOnError false
+    }
+    sourceSets {
+        main {
+            manifest.srcFile './ApplicationManifest.xml'
+        }
+    }
+    externalNativeBuild {
+        cmake {
+            path './CMakeLists.txt'
+            //'rsocket-cpp-0.10.0/CMakeLists.txt'
+        }
+    }
+}
+//'x86', 'x86_64', 'armeabi-v7a',