Support for gradle and gradle.kts extensions

[sgarfinkel]

The *.gradle extension should be interpreted as Groovy. The *.gradle.kts should be interpreted as Kotlinscript (I think this might be a limitation of the underlying source code highlighter, which doesn't properly highlight these extensions).

Instead of doing ad-hoc *.gradle.kts it might be more helpful to just highlight all *.kts extensions as standard Kotlin *.kt files.