Support Kotlin-based Gradle files

Currently, the `gradle` operation and Gradle API features only support Groovy. This is because the Groovy language ships with a [parser API](http://docs.groovy-lang.org/2.3.5/html/api/org/codehaus/groovy/ast/package-summary.html) that can be used to accurately modify the actual Gradle source file. As far as I know, no such API exists for Kotlin.

Creating an issue to track this and in case anyone knows of a similar Kotlin API