Added Vagrant configuration cookbook

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | yes
| Applies to    | all
| Fixed tickets | n/a

A new cookbook article was added with an example Vagrant configuration that can be used with the Symfony Standard Edition.
It seems like Hashicorp did not prepare `trusty32` or `trusty64` packages specifically, but if you look at the list at https://vagrantcloud.com/discover/featured there are references to `ubuntu/trusty32` and `ubuntu/trusty64` which could be used.  I believe this type of vendor/package name reference was introduced with Vagrant 1.5.  It is possible to update the Vagrantfile `config.vm.box` value to use one of these references and remove the `config.vm.box_url` line entirely (since it will no longer be necessary).  If we would like to incorporate one of these to be up-to-date as @timglabisch suggests, I'd like to test the configuration to make sure it still works.