install pre-commit hook that formats via spotless

[stefanlack]

Is your feature request related to a problem? Please describe. We use spotlessJavaCheck on travis to verify that code is formatted according to the rules. Since my IDE does not exactly format in the same way, I have to run gradle spotlessJavaApply manually. Sometimes I do forget to run the formatter.

Describe the solution you'd like Implement a pre-commit hook that runs gradlew spotlessJavaApply. Installation of the hook can be easyly automated via gradle, for example https://gist.github.com/KenVanHoeylandt/c7a928426bce83ffab400ab1fd99054a

@michaelsauter @tjaeschke Whats do you think?

[tjaeschke]

I think this is a good idea, since I have the same problem.