Update Android build script to Android Studio/Gradle's ndkBuild plugin

[ggfan]

Update the build to ndkBuild as ndk-build scripts are already there in the source tree. This would allow:

• building with current Android Studio/Gradlew
• future compatible for Android Studio Gradle-experimental is out of support at least for now.

Please test it on your device: I do not have the device environment.

Once this is merged in, .gitignore needs to be updated to ignore studio tmp files:

• */.iml
• **/build
• **/.externalNativeBuild

(it needs this to be in first I think )

Thanks

[kamrik]

Thanks!