Add annotation processor for @ReactProp

Summary:
The annotation processor finds subclasses of ViewManager and ShadowNode and generates classes that can both provide a mapping of property names to their type as well as a way of setting these properties.

This avoids having to do reflection to find the properties.

The annotation processor is currently not working when building with Gradle.

public

Reviewed By: astreet

Differential Revision: D2748958

fb-gh-sync-id: ded5b072d236ebf19fb43eaf704fc7f221a82c26

Author: lexs

ReactAndroid/build.gradle

@@ -227,6 +227,9 @@ android {
         jni.srcDirs = []
         jniLibs.srcDir "$buildDir/react-ndk/exported"
         res.srcDirs = ['src/main/res/devsupport', 'src/main/res/shell']
+        java {
+          exclude 'com/facebook/react/processing'
+        }
     }
 
     tasks.withType(JavaCompile) {