Travis CI: run PHP 5.3 first

The code sniff pass runs on PHP 5.3 so we should run it first so that
we can be aware of failures as soon as possible.

See #6
Standardize textdomains

See #7
Add wp-l10n-validator config

See #7
Use WordPoints' PHPCS rules for Travis

See #6
Travis CI: set up the WordPoints tests dir

See #6