Use deterministic code formatter

[ppkarwasz]

It would nice to have a deterministic way to format code in PRs.

There are surely as many opinion on this as there are developers, but my personal favorite is palantir-java-formatter, because:

• It uses 4 spaces of indentation (google-java-formatter IIRC uses 2).
• It does not have any options, unlike the Eclipse formatter, which prevents never ending discussions on each option.
• It has plugins for major IDEs (IntelliJ IDEA and Eclipse) and can also run using the Spotless Maven Plugin to both check and fix the formatting.

[jeremylong]

I'd be good with Spotless + palantir-java-formatter.

[ppkarwasz]

I'll make a PR then.