Updated gradle + plugins

Updated Gradle, Gradle plugin and Bintray plugin to newest versions.
Added realm-annotation-processor project to settings.gradle, so it appears as a editable project inside Android Studio.

Note: You might have to delete the .gradle folder inside the project after updating to avoid the following error:

````
org.gradle.api.internal.changedetection.state.DefaultFileCollectionSnapshotter$FileCollectionSnapshotImpl cannot be cast to org.gradle.api.internal.changedetection.state.OutputFilesCollectionSnapshotter$OutputFilesSnapshot
````

OK, but I don't think I noticed any problems in AndroidStudio 0.8.13. What issues have you run into?