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.