Update Gradle to version 1.0.0

@crankycoder This fixes #1327 
The `versionCode` and `versionName` are set automatically from the `build.gradle` file, so I removed the custom code.
Regarding the `PackageUtils` change: for testing I modified the version and `applicationId` and checked if the app version was still displayed correctly. Everything seems fine.
Do you see any problems with this?