Implement Comprehensive Lint Engine

Summary:
This adds a new lint engine, ComprehensiveLintEngine, which
includes sane defaults for some generic languages.

Ideally this would include *all* available language linters,
but that can be enhanced at a later point. Right now it's mostly
the base linter with additional JavaScript and Python linters.

Test Plan:
Adjust the lint_engine to be "ComprehensiveLinterEngine". You'll
also need jshint, pyflakes, and pep8 to all be available on PATH.

Run arc lint against files which contain .php, .py, and .js.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran

Differential Revision: https://secure.phabricator.com/D1439