Expose remotely available gradle versions via the tooling api

Consider the situation when end-user works with the gradle via application, which in turn uses tooling api. It seems convenient to allow end-user to choose target gradle version to work with. The actions sequence looks like below then:

1. Intermediate application asks the tooling api about remotely available gradle versions;
2. The application shows GUI with the available versions to the end-user;
3. End-user selects target gradle version he or she wants to work with;
4. The application downloads target version (GradleConnector.useDistribution());