Adding a vagrantfile and documentation.

This sets up a 14.04 x86_64 vm and sets up girder under nginx. With this
setup, girder is used for the dynamic contents (the API) and nginx is used
for the static resources (javascript, one-page-app, etc). This should be
amenable to modifications for use in a general deployment.
Merge pull request #232 from girder/vagrant

Adding a vagrantfile and documentation.