Require PHP >5.4.15

The version of PHP listed in the composer.json was not the same
as the version of PHP installed on the Vagrant box. This is open
for discussion, obviously, but I would like this project to push
anyone wanting to use it to upgrade from 5.2 or 5.3 to 5.4 (or
possibly 5.5 depending on timeline).
Installing composer deps via provision

Adding manifests to install composer on the vagrant box and run
the installation via composer during provision. This eliminates
the need to run the composer install step during the "Installation"
or "quick start" as well as having to set up a PHP environment
locally.