Arcanist linter configuration

Summary:
This configuration forks the configuration I wrote for rNOTIF.

It allows to use minimal lint check (spelling, JSON, php -l).

To use phpcs isn't really useful here, as WP-CLI conventions
don't follow PSR-1.

Test Plan: arc lint --everything

Reviewers: dereckson

Maniphest Tasks: T887

Differential Revision: http://devcentral.nasqueron.org/D437