When reviewing https://github.com/Kotlin/dataframe/pull/516 I noticed we didn't have a linter enabled for all modules. This PR enabled kotlinter for all modules (except jdbc as @zaleslaw is actively working on it), plus it fixes any linting issues encountered along the way.
Fixes https://github.com/Kotlin/dataframe/issues/520.
When reviewing https://github.com/Kotlin/dataframe/pull/516 I noticed we didn't have a linter enabled for all modules. This PR enabled kotlinter for all modules (except jdbc as @zaleslaw is actively working on it), plus it fixes any linting issues encountered along the way.