Upgrade Gradle wrapper and sonarqube plugin

[davidmichaelkarr]

This is wrappered to version Gradle 3.2.1, which is pretty old. If I try to import it into Eclipse with a more recent version of Gradle, it fails with an error described at the following: https://github.com/gradle/gradle/issues/1667 .

The fix, as described on that page, is simply to upgrade the sonarqube plugin from 2.2 to a more recent version, like 2.5.

It would also be good to change the gradle version in the wrapper to a more recent version.