Bump gradle and android dependencies

Summary:
We need to use the most recent Android SDK to leverage the cmake-based NDK build
system. Also, since everything seems to be still working - why not?

I also changed the dependency of `yoga-layout` to be the project, not the
pre-published artifact as it no longer compiled due to the changed measure API
signature. I'm not sure if there was a reason to keep the two separate.

By relying on Maven-published artifacts, we generate better POMs when publishing
and people can override dependencies and see them more easily.

A few more cleanups based on what we did with Litho.

Reviewed By: emilsjolander

Differential Revision: D4913208

fbshipit-source-id: 053deb444ce91106afb3b66c3be28d6fcbdea450

build.gradle

@@ -18,15 +18,18 @@ buildscript {
 allprojects {
   repositories {
     jcenter()
-    flatDir {
-      dirs "${rootDir}/lib/jsr-305"
-      dirs "${rootDir}/lib/soloader"
-      dirs "${rootDir}/lib/appcompat"
-      dirs "${rootDir}/lib/android-support"
-    }
   }
 }
 
+ext {
+    minSdkVersion = 15
+    targetSdkVersion = 25
+    compileSdkVersion = 25
+    buildToolsVersion = '25.0.2'
+    sourceCompatibilityVersion = JavaVersion.VERSION_1_7
+    targetCompatibilityVersion = JavaVersion.VERSION_1_7
+}
+
 task clean(type: Delete) {
     delete rootProject.buildDir
 }