Update for Android Studio 1.0, better documentation

- Updated Gradle configs for Android Studio 1.0.2.
- Duplicated Gradle variables (e.g. minSdkVersion) in `ParseLoginUI` library project so that the developer won't have to redefine them when they import the library.
- Added section in README specifically for importing `ParseLoginUI` into the developer's own app.
- Updated license.
- Updated Parse SDK, Facebook SDK, and Bolts library to latest.