QtQ4A: Copy Gradle wrapper from Qt installation

Why?

We're currently finding a Gradle executable from the Gradle cache under ~/.gradle. While this works there is a chance it might break due to a change in the environment. A standard Qt installation comes with a copy of the Gradle wrapper which can easily be copied to the example directory (like we already do in QtGP RTA).

What?

Copy the code from QtGP RTA and use it in QtQ4A RTA.