Add php::ensure parameter

This adds a new parameter `$ensure` to the base class `php`, which is passed to all package resources in the module. Every component can stil be overriden with hiera if needed, for example `php::cli::ensure` or `php::fpm::ensure' if different versions are needed. This fixes #25.

Due to dependency fuckups (unversioned dependencies) in Ubuntu, I had to add the new class `php::packages` to install the common packages before the the other PHP components.

:warning: This was only tested on Ubuntu for now!