Make wart remover and ScalaJS play nicely

[outkaj]

Wart remover and Scala JS don't play well together - wart remover thinks JsExport, etc are signs of an error. There used to be a wart remover plugin specifically for ScalaJS, but it seems deprecated. At some point we should still enable Wart Remover for the project (we may have to make a custom ruleset disabling some of their basic rules).

[adridadou]

Let's push that for later. It's not very important for now because openlaw-client doesn't have that much code anyway.