Replace TravisCI base box with precise64 base box. 

The core of this change is to start Vagrant with a basic `precise64` box instead of starting with a TravisCI base box and building a custom box from that. The main goal of this change is to support multiple Vagrant providers, such as the [VMware Fusion provider](http://www.vagrantup.com/vmware) and the [AWS provider](https://github.com/mitchellh/vagrant-aws). The TravisCI base box is VirtualBox-specific which makes it difficult to support other Vagrant providers. 

Other changes in this PR are: 

* Use [Berkshelf](http://berkshelf.com/) instead of copying external Chef recipes into the project repo. 
* Add `warden` as a sub-module and set it up under `/vagrant/warden`. This was previously set up in the custom TravisCI base box in `/warden`. 
* Add uaa as a sub-module instead of doing a `git checkout` in the `rake cf:bootstrap` task. Do a `mvn package` of uaa in the `rake cf:bootstrap` task so that most Maven dependencies get downloaded at build time instead of when `foreman start` is run.

Please comment on the individual changes as necessary.