Add modified PSR2 ruleset for spec/* linting

Summary:
Add spec/ruleset.xml - uses PSR2 with exceptions for method scope and camelCase
Add arc lint rules to lint specs separately

Test Plan:
Modify some specs, run arc lint
Modify src/, run arc lint.

Reviewers: shadowhand

Reviewed By: shadowhand

Differential Revision: https://phabricator.ushahidi.com/D312