[PR] Install and configure PHP 5.5 and other goodies during initial provisioning

* [x] Updates the PPA to use latest PHP 5.5 stable.
* [x] Removes the unsupported php-apc package and custom APC config.
* [x] Provides a custom opcache.ini, which enables Zend Opcache.
* [ ] Provide a custom php5-fpm.conf, something we haven't yet done.
* [ ] Add an Opcache monitoring tool - [opcache-status](https://github.com/rlerdorf/opcache-status)

This will work best on new provisions. It's possible that strange things could happen with a `vagrant provision` on an existing machine, as APC will no longer be provided, PHP won't be upgraded, and Opcache will all of a sudden be there. It will probably work anyway.

That all said—do `vagrant destroy` and `vagrant up` for ultimate happiness.

Fixes #197