Upgrade to official build tools 1.0 and add gradle wrapper.

The wrapper is for people who might be on Windows or not used to a gradle build system. They can just run commands with ./gradlew instead of having to install gradle themselves.

Sorry for so many PR's so quickly! Not sure if you wanted them in bigger pieces or smaller ones :\
AndroidManifest is ignored because this library could be part of a larger project that has a manifest, that we don't want included in the repo.