Simplify Vagrantfile - read group_vars/development

Previously there was some duplication between configuring the `Vagrantfile` and also `group_vars/development`. Another downside was the Ansible playbook supports multiple sites but the `Vagrantfile` did nothing to easily allow that.

Now the `Vagrantfile` will read `group_vars/development` and automatically set up all the hosts and synced folders. The only addition needed for this is setting `local_path` on each site.

@fullyint love to get your thoughts on this.
(editing the two lines above...)
"Whenever you move or copy the `Vagrantfile` somewhere else, you need to make sure to adjust `ANSIBLE_PATH` (in `Vagrantfile`) and `local_path` (in `group_vars/development`)."