Add an `ArcanistJscsLinter`.

Summary: Add a linter which wraps around [[https://github.com/mdevils/node-jscs | JSCS]].

Test Plan: Currently, we can't test this linter with out existing infrastructure. Specifically, `jscs` will only lint `*.js` files. I have done a fair bit of manual testing though.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9565